Filed Pursuant to Rule 424(b)(5)
Registration No. 333-268340

PROSPECTUS SUPPLEMENT

(To Prospectus dated November 14, 2022)

8,000,000 Shares

Portillo’s Inc.

Class A Common Stock

We are offering 8,000,000 shares of our Class A common stock.

We intend to use all of the net proceeds from this offering to purchase LLC Units (as defined herein) from certain Continuing Pre-IPO LLC Members (as defined herein) and to repurchase shares of Class A common stock from the Reorganization Parties (as defined herein) (together such Continuing Pre-IPO LLC Members and such Reorganization Parties, the “selling stockholders”) in a “synthetic secondary” transaction, at a price per LLC Unit or share of Class A common stock, as applicable, equal to the public offering price per share of Class A common stock in this offering, less the underwriting discounts and commissions and any withholding taxes. As a result, Portillo’s OpCo will not receive any proceeds from this offering. See “Use of Proceeds”.

Our Class A common stock is listed on Nasdaq Global Select Market (the “Nasdaq”) under the symbol “PTLO.” On November 11, 2022, the last sale price of our Class A common stock as reported on Nasdaq was $25.41 per share.

We have two classes of common stock: Class A common stock and Class B common stock. Each share of Class A common stock and Class B common stock entitles its holder to one vote on all matters presented to our stockholders generally. All of our Class B common stock is held by the Continuing Pre-IPO LLC Members on a one-to-one basis with the number of LLC Units they own. See “Description of Capital Stock” in the accompanying prospectus. As a result, the Reorganization Parties and Continuing Pre-IPO LLC Members, together, control any action requiring the general approval of our stockholders, including the election of our Board of Directors (the “Board”), the adoption of amendments to our certificate of incorporation and bylaws and the approval of any merger or sale of the Company or substantially all of our assets.

We are an “emerging growth company” as defined under the federal securities laws and, as such, will be subject to reduced public company reporting requirements.

Investing in our Class A common stock involves a high degree of risk. See “Risk Factors” on page S-12.

The underwriters have agreed to purchase the Class A common stock from us at a price of $22.69 per share, which will result in $181,520,000 of proceeds before expenses. The underwriters may offer the shares of Class A common stock from time to time for sale in one or more transactions on Nasdaq, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices. See “Underwriting” for additional information regarding underwriter compensation.

We have granted the underwriters an option to purchase up to an additional 1,200,000 shares from us at the purchase price at any time within 30 days from the date of this prospectus supplement.

Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares against payment in New York, New York on November 17, 2022.

The date of this prospectus supplement is November 14, 2022.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering of Class A common stock and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. Generally, when we refer to this prospectus supplement, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or in any document incorporated by reference that was filed with the SEC, before the date of this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

You should rely only on the information contained in this prospectus supplement, the accompanying prospectus or in any free writing prospectus we may specifically authorize to be delivered or made available to you. Neither we nor the underwriters (or any of our or their respective affiliates) have authorized anyone to provide any information other than that contained in this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you. Neither we nor the underwriters (or any of our or their respective affiliates) take any responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We and the underwriters (or

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any of our or their respective affiliates) are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, or any free writing prospectus is accurate only as of its date, regardless of its time of delivery or the time of any sale of shares of our Class A common stock. Our business, financial condition, results of operations and prospects may have changed since that date.

For investors outside the United States: We and the underwriters have not done anything that would permit this offering or the possession or distribution of this prospectus supplement, the accompanying prospectus or any free writing prospectus we may provide to you in connection with this offering in any jurisdiction where action for purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the shares of Class A common stock and the distribution of this prospectus supplement outside the United States. See “Underwriting.”

As permitted under the rules of the SEC, this prospectus supplement incorporates important business information about Portillo’s OpCo that is contained in documents that we file with the SEC, but that is not included in or delivered with this prospectus supplement. You may obtain copies of these documents, without charge, from the website maintained by the SEC at www.sec.gov, as well as from other sources. See “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference” in this prospectus supplement.

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BASIS OF PRESENTATION

As used in this prospectus supplement, unless otherwise noted or the context requires otherwise:

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Certain statements made in this prospectus supplement, the documents that are incorporated by reference in this prospectus supplement and other written or oral statements made by or on behalf of Portillo’s may constitute “forward-looking statements” within the meaning of the “safe harbor” provisions of the United States Private Securities Litigation Reform Act of 1995 which are subject to known and unknown risks, uncertainties and other important factors that may cause actual results to be materially different from the statements made herein. All statements other than statements of historical fact are forward-looking statements. You can identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. These statements may include words such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “future,” “outlook,” “potential,” “project,” “projection,” “plan,” “intend,” “seek,” “may,” “could,” “would,” “will,” “should,” “can,” “can have,” “likely,” the negatives thereof and other similar expressions. These forward-looking statements are based only on our current beliefs, expectations and assumptions regarding the future of our business, future plans and strategies, projections, anticipated events and trends, the economy and other future conditions and speak only as of the date on which it is made. Many of the forward-looking statements are located in “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” which may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to, the following:

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This list of factors that may affect future performance and the accuracy of forward-looking statements is illustrative but not exhaustive. In addition, new risks and uncertainties may arise from time to time. Accordingly, all forward-looking statements should be evaluated with an understanding of their inherent uncertainty and we caution accordingly against relying on forward-looking statements.

Consider these factors carefully in evaluating the forward-looking statements. For further information about these and other risks and uncertainties as well as strategic initiatives, see “Risk Factors” in our Annual Report (as defined in this prospectus supplement) and subsequent reports filed by us with the SEC, including on Form 8-K.

All subsequent written and oral forward-looking statements attributable to us or persons acting on our behalf are expressly qualified in their entirety by these cautionary statements. The forward-looking statements included herein are made only as of the date hereof, and we do not undertake any obligation to release publicly any revisions to such forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

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RISK FACTORS

An investment in our Class A common stock involves a high degree of risk. You should carefully consider each of the following risk factors, together with the other information contained in this prospectus supplement, the accompanying prospectus and the information incorporated by reference in this prospectus supplement, including the risk factors included in “Part I. Item 1A. Risk Factors” in our Annual Report (as defined in this prospectus supplement) and other reports we file with the SEC, before investing in our Class A common stock. The occurrence of any of the following risks could materially and adversely affect our business, prospects, financial condition, results of operations and cash flow, in which case the trading price of our Class A common stock could decline and you could lose all or part of your investment. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also impair our business, prospects, financial condition, results of operations and cash flow. See “Cautionary Note Regarding Forward-Looking Statements” elsewhere in this prospectus supplement.

Risks Related to this Offering and Ownership of Our Class A Common Stock

Future offerings of debt or equity securities by us may have a material adverse effect on the market price of our Class A common stock.

In the future, we may attempt to obtain financing or to further increase our capital resources by issuing additional shares of our Class A common stock or by offering debt or other equity securities, including senior or subordinated notes, debt securities convertible into equity or shares of preferred stock.

Any future debt financing could involve restrictive covenants relating to our capital-raising activities and other financial and operational matters, which might make it more difficult for us to obtain additional capital and to pursue business opportunities, including potential acquisitions. Moreover, if we issue debt securities, the debt holders would have rights to make claims on our assets senior to the rights of our holders of our Class A common stock. The issuance of additional shares of our Class A common stock or other equity securities or securities convertible into equity may dilute the economic and voting rights of our existing stockholders or reduce the market price of our Class A common stock or both. Debt securities convertible into equity could be subject to adjustments in the conversion ratio pursuant to which certain events may increase the number of equity securities issuable upon conversion. Preferred shares, if issued, could have a preference with respect to liquidating distributions or a preference with respect to dividend payments that could limit our ability to pay dividends to the holders of our Class A common stock. Our decision to issue securities in any future offering will depend on market conditions and other factors beyond our control, which may have a material adverse effect on the amount, timing, or nature of our future offerings. Thus, holders of our Class A common stock bear the risk that our future offerings may reduce the market price of our Class A common stock and dilute their stockholdings in us.

If the ownership of our Class A common stock continues to be highly concentrated, it may prevent you and other minority stockholders from influencing significant corporate decisions and may result in conflicts of interest. Although we will no longer be a “controlled company” within the meaning of the rules of the Nasdaq following this offering, our principal investors will continue to exert substantial influence over us.

Following the closing of this offering, funds managed by Berkshire are expected to own (i) approximately 41.8% of the combined voting power of our common stock (or approximately 40.2% of the combined voting power of our common stock, if the underwriters exercise their option to purchase additional shares of Class A common stock in full) and (ii) approximately 41.8% of the economic interest in Portillo’s OpCo (or approximately 40.2% of the economic interest in Portillo’s OpCo if the underwriters exercise their option to purchase additional shares of Class A common stock in full). As a result, we will no longer be a “controlled company” within the meaning of the Nasdaq listing rules. Nevertheless, Berkshire will indirectly beneficially own shares sufficient to significantly influence all matters requiring stockholder votes, including: the election of directors; mergers, consolidations and acquisitions; the sale of all or substantially all of our assets and other decisions affecting our capital structure; amendments to our certificate of incorporation or our bylaws; and our winding up and dissolution.

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This concentration of ownership may delay, deter or prevent acts that would be favored by our other stockholders. The interests of Berkshire may not always coincide with our interests or the interests of our other stockholders. This concentration of ownership may also have the effect of delaying, preventing or deterring a change in control of us. Also, Berkshire may seek to cause us to take courses of action that, in its judgment, could enhance its investment in us, but which might involve risks to our other stockholders or adversely affect us or our other stockholders, including investors in this offering. As a result, the market price of our Class A common stock could decline or stockholders might not receive a premium over the then-current market price of our Class A common stock upon a change in control. In addition, this concentration of share ownership may adversely affect the trading price of our Class A common stock because investors may perceive disadvantages in owning shares in a company with significant stockholders. See “Description of Capital Stock—Anti-takeover Provisions” in the accompanying prospectus.

The Tax Receivable Agreement with the TRA Parties requires us to make cash payments to them in respect of certain tax benefits to which we may become entitled, and we expect that the payments we will be required to make will be substantial.

Under the Tax Receivable Agreement, we are required to make cash payments to the TRA Parties equal to 85% of the tax benefits, if any, that we actually realize, or in certain circumstances are deemed to realize, as a result of (i) our allocable share of existing tax basis in depreciable or amortizable assets related to LLC Units acquired in the IPO, (ii) certain favorable tax attributes we acquired from the Blocker Companies in the Mergers (including net operating losses and the Blocker Companies’ allocable share of existing tax basis), (iii) increases in our then allocable share of existing tax basis in depreciable or amortizable assets, and adjustments to the tax basis of the tangible and intangible assets, of Portillo’s OpCo and its subsidiaries, as a result of (x) sales or exchanges of interests in Portillo’s OpCo (including repayment of the redeemable preferred units) in connection with the IPO and (y) future redemptions or exchanges of LLC Units by Continuing Pre-IPO LLC Members for cash or Class A common stock, including in connection with this offering and (iv) certain other tax benefits related to entering into the Tax Receivable Agreement, including payments made under the Tax Receivable Agreement.

Based on several assumptions, it was estimated that, as of September 25, 2022, our obligation for future payments under the Tax Receivable Agreement totaled $205.3 million. Amounts payable under the Tax Receivable Agreement are contingent upon, among other things, (i) generation of future taxable income over the term of the Tax Receivable Agreement and (ii) future changes in tax laws. If we do not generate sufficient taxable income in the aggregate over the term of the Tax Receivable Agreement to utilize the tax benefits, then we would not be required to make the related Tax Receivable Agreement payments. The payments that we are required to make will generally reduce the amount of overall cash flow that might have otherwise been available to us, but we expect the cash tax savings we will realize to fund the required payments. Assuming no material changes in relevant tax law and that we earn sufficient taxable income to realize all tax benefits that are subject to the Tax Receivable Agreement, we estimate that the tax savings associated with all tax attributes described above would aggregate to approximately $241.5 million as of September 25, 2022. Under this scenario, we would be required to pay the TRA Parties approximately 85% of such amount, or $205.3 million, primarily over the next 15 years, substantially declining in year 16 through year 47. The actual amounts we will be required to pay may materially differ from these hypothetical amounts, because potential future tax savings that we will actually realize or be deemed to realize, and the Tax Receivable Agreement payments made by us, will be calculated based in part on the market value of our Class A common stock at the time of each exchange of an LLC Unit for a share of Class A common stock and the prevailing applicable federal tax rate (plus the assumed combined state and local tax rate) applicable to us over the life of the Tax Receivable Agreement and will depend on our generating sufficient taxable income to realize the tax benefits that are subject to the Tax Receivable Agreement.

Payments under the Tax Receivable Agreement will be based on the tax reporting positions we determine, and the IRS or another taxing authority may challenge all or part of the existing tax basis, deductions, tax basis increases, net operating losses or other tax attributes subject to the Tax Receivable Agreement, and a court could

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sustain such challenge. Payments we will be required to make under the Tax Receivable Agreement generally will not be reduced as a result of any taxes imposed on us, Portillo’s OpCo or any direct or indirect subsidiary thereof that are attributable to a tax period (or portion thereof) ending on or before the Mergers or the date of the completion of the IPO. Further, the TRA Parties will not reimburse us for any payments previously made if such tax attributes are subsequently challenged by a taxing authority and are ultimately disallowed, except that any excess payments made to a TRA Party will be netted against future payments otherwise to be made to such TRA Party under the Tax Receivable Agreement, if any, after our determination of such excess. As a result, in such circumstances we could make future payments under the Tax Receivable Agreement that are greater than our actual cash tax savings and may not be able to recoup those payments, which could negatively impact our liquidity. See “Part I. Item 1A. Risk Factors—Risks Related to Our Organizational Structure—We will not be reimbursed for any payments made to the TRA Parties under the Tax Receivable Agreement in the event that any tax benefits are disallowed” in our Annual Report.

Our obligations under the Tax Receivable Agreement will also apply with respect to any person who is issued LLC Units in the future and who becomes a party to the Tax Receivable Agreement.

We are a holding company with no operations of our own and our ability to make payments under the Tax Receivable Agreement will depend on the ability of Portillo’s OpCo to make distributions to us. Deterioration in the financial condition, earnings, or cash flow of Portillo’s OpCo and its subsidiaries for any reason could limit or impair their ability to pay such distributions. To the extent that we are unable to make payments under the Tax Receivable Agreement for any reason, such payments generally will be deferred and will accrue interest until paid. Nonpayment for a specified period, however, may constitute a breach of a material obligation under the Tax Receivable Agreement and therefore accelerate payments due under the Tax Receivable Agreement (unless, generally, such nonpayment is due to a lack of sufficient funds) which could negatively impact our results of operations and could also affect our liquidity in periods in which such payments are made.

We do not anticipate paying any dividends on our Class A common stock in the foreseeable future.

We do not expect to declare or pay any cash or other dividends in the foreseeable future on our Class A common stock because we intend to use cash flow generated by operations to grow our business. Our Credit Facilities do not restrict our ability to pay cash dividends on our Class A common stock but they may restrict the ability of certain subsidiaries of Portillo’s OpCo to pay such cash dividends to Portillo’s OpCo. We may also enter into other credit agreements or other borrowing arrangements in the future that restrict or limit our ability to pay cash dividends on our Class A common stock. As a result, you may not receive any return on an investment in our Class A common stock unless you sell our Class A common stock for a price greater than that which you paid for it. See “Dividend Policy” in the accompanying prospectus.

Our quarterly results of operations may fluctuate significantly and could fall below the expectations of securities analysts and investors due to seasonality and other factors, some of which are beyond our control, resulting in a decline in our stock price.

Our quarterly results of operations may fluctuate due principally to seasonal factors and the timing of holidays. Accordingly, results for any one quarter are not necessarily indicative of results to be expected for any other quarter or for any year and same-restaurant sales for any particular future period may decrease. In addition, as we expand our number of restaurants in hot weather climates, the seasonality of our business may be amplified due to a portion of the population who lives elsewhere in the summer. Similarly, our plans to expand the number of restaurants in cold weather climate could be impacted by the population heading south for the summer. In the future, results of operations may fall below the expectations of securities analysts and investors. In that event, the price of our Class A common stock could be adversely impacted.

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The market price and trading volume of our Class A common stock has been, and may in the future, be volatile, which could result in rapid and substantial losses for our stockholders, and you may lose all or part of your investment.

Shares of our Class A common stock sold in this offering may experience significant volatility on the Nasdaq. An active, liquid and orderly market for our Class A common stock may not be sustained, which could depress the trading price of our Class A common stock or cause it to be highly volatile or subject to wide fluctuations. The market price of our Class A common stock has fluctuated and may fluctuate or may decline significantly in the future and you could lose all or part of your investment. Some of the factors that could negatively affect our share price or result in fluctuations in the price or trading volume of our Class A common stock include:

These broad market and industry factors may decrease the market price of our Class A common stock, regardless of our actual financial performance. The stock market in general has from time to time experienced extreme price and volume fluctuations, including recently. In addition, in the past, following periods of volatility

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in the overall market and decreases in the market price of a company’s securities, securities class action litigation has often been instituted against these companies. This litigation, if instituted against us, could result in substantial costs and a diversion of our management’s attention and resources, which could have a material adverse effect on our business, financial condition and results of operations.

The future issuance of additional Class A common stock in connection with any equity plans, acquisitions or other sales of substantial amounts of our Class A common stock in the public markets will dilute all other stockholdings and could negatively affect the market price of our Class A common stock.

We may issue all these shares of Class A common stock without any action or approval by our stockholders, subject to certain exceptions. Any Class A common stock issued in connection with any equity incentive plan, the exercise of outstanding stock options, or otherwise, would dilute the percentage ownership held by the investors who purchase Class A common stock in this offering. Additionally, of our issued and outstanding shares, all the Class A common stock sold in this offering will be freely transferable, except for any shares held by our “affiliates,” as that term is defined in Rule 144 under the Securities Act. Following the closing of this offering, approximately 41.8% of our Class A common stock on an as-converted basis, will be beneficially owned by funds managed by Berkshire, and can be resold into the public markets in the future in accordance with the requirements of Rule 144. See “Shares Eligible For Future Sale” in the accompanying prospectus.

For as long as we are an emerging growth company, we will not be required to comply with certain reporting requirements, including those relating to accounting standards and disclosure about our executive compensation, that apply to other public companies.

We are an emerging growth company, as defined in Section 2(a) of the Securities Act, as modified by the JOBS Act, and we have elected to take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. These provisions include, but are not limited to, not being required to comply with the auditor attestation requirements of Section 404(b) of the Sarbanes Oxley Act, reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a non-binding advisory vote on executive compensation and of stockholder approval of any golden parachute payments not previously approved. We do not know if some investors will find our Class A common stock less attractive as a result of our decision to avail ourselves of certain of these exemptions. The result may be a less-active trading market for our Class A common stock and our stock price may be more volatile.

In addition, Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities Act for complying with new or revised accounting standards. In other words, an emerging growth company can delay the adoption of certain accounting standards until those standards would otherwise apply to private companies. We have elected to avail ourselves of this exemption and, therefore, we can delay the adoption of certain accounting standards until those standards would otherwise apply to private companies.

We could remain an emerging growth company for up to five years or until the earliest of (a) the last day of the first fiscal year in which our annual gross revenues exceed $1.235 billion, (b) the date that we become a large accelerated filer as defined in Rule 12b-2 under the Exchange Act, which would occur if the market value of our common stock that is held by non-affiliates exceeds $700 million as of the last business day of our most recently completed second fiscal quarter, or (c) the date on which we have issued more than $1 billion in non-convertible debt securities in the preceding three-year period.

The exact implications of the JOBS Act are still subject to interpretations and guidance by the SEC and other regulatory agencies, and we cannot assure you that we will be able to take advantage of all of the benefits of the JOBS Act. In addition, investors may find our Class A common stock less attractive to the extent we rely on the exemptions and relief granted by the JOBS Act. If some investors find our Class A common stock less attractive as a result, there may be a less active trading market for our Class A common stock and our stock price may decline or become more volatile.

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USE OF PROCEEDS

We estimate that the net proceeds to us from our sale of 8,000,000 shares of Class A common stock in this offering will be $181,520,000 based on the purchase price set forth on the cover of $22.69 per share, before deducting any estimated expenses payable by us in connection with this offering.

We intend to use all of the net proceeds from this offering to purchase or cancel, as the case may be, LLC Units or shares of Class A common stock, as applicable, of the selling stockholders in a “synthetic secondary” transaction, at a price per LLC Unit or share of Class A common stock, as applicable, equal to the purchase price set forth on the cover less any withholding taxes. As a result, Portillo’s OpCo will not receive any proceeds from this offering.

The underwriters also have an option to purchase up to an additional 1,200,000 shares of Class A common stock from us. We estimate that the net proceeds to us, if the underwriters exercise their right to purchase the maximum of additional shares of Class A common stock from us, will be $208,748,000 based on the purchase price set forth on the cover of $22.69 per share, before deducting any estimated expenses payable by us in connection with this offering. We will use the additional net proceeds we receive pursuant to any exercise of the underwriters’ option to purchase additional LLC Units or shares of Class A common stock from the selling stockholders.

We estimate that the offering expenses will be approximately $1,100,000. All of such offering expenses will be paid for or otherwise borne by Portillo’s OpCo.

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UNAUDITED PRO FORMA CONSOLIDATED FINANCIAL INFORMATION

We have derived the unaudited consolidated pro forma statement of operations for the year ended December 26, 2021 set forth below by the application of pro forma adjustments to the audited consolidated financial statements of Portillo’s Inc. and its subsidiaries included in our Annual Report, which is incorporated by reference herein. We have derived the unaudited consolidated pro forma statement of operations for the three quarters ended September 25, 2022 set forth below by the application of pro forma adjustments to the unaudited consolidated financial statements of Portillo’s Inc. and its subsidiaries included in our quarterly report on Form 10-Q for the quarterly period ended September 25, 2022, filed with the SEC on November 3, 2022 (the “2022 Q3 Quarterly Report”), which is incorporated by reference herein.

The following unaudited pro forma consolidated statement of operations for the year ended December 26, 2021 give effect to the pro forma adjustments related to (i) the IPO and the Reorganization Transactions, which we refer to as the “IPO and Reorganization Transactions,” (ii) the offering and sale of 8,066,458 shares of Class A common stock at an offering price of $23.75 per share and the application of the net proceeds from such offering, which we refer to as the “August Secondary Offering” and (iii) the offering and sale of 8,000,000 shares of Class A common stock (excluding shares issuable upon exercise of the underwriters’ option to purchase additional shares, if any) at an offering price of $22.69 per share and the application of the net proceeds from such offering, which we refer to as the “November Secondary Offering,” as if all such transactions had been completed as of December 28, 2020. We refer to the August Secondary Offering and the November Secondary Offering collectively as the “Secondary Transactions.” The unaudited pro forma consolidated statement of operations for the three quarters ended September 25, 2022 presents our consolidated results of income to give pro forma effect to the Secondary Transactions, as if all such transactions had been completed as of December 27, 2021.

The unaudited pro forma balance sheet as of September 25, 2022 presents our financial position to give pro forma effect to the November Secondary Offering, as if it had occurred on September 25, 2022.

The unaudited pro forma financial information has been prepared by our management and is based on Portillo’s Inc. historical financial statements and the assumptions and adjustments described in the notes to the unaudited pro forma financial information below. The presentation of the unaudited pro forma financial information is prepared in conformity with Article 11 of Regulation S-X rules effective January 1, 2021.

We based the pro forma adjustments on available information and on assumptions that we believe are reasonable under the circumstances in order to reflect, on a pro forma basis, the impact of the relevant transactions on the historical financial information of Portillo’s. See the notes to unaudited pro forma financial information below for a discussion of assumptions made. The unaudited pro forma financial information does not purport to be indicative of our results of operations or financial position had the relevant transactions occurred on the dates assumed and does not project our results of operations or financial position for any future period or date.

The IPO and Reorganization Transactions adjustments are described in the notes to the unaudited pro forma consolidated financial information and primarily include:

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The Secondary Transactions adjustments are described in the notes to the unaudited pro forma consolidated financial information and primarily include:

The unaudited pro forma consolidated financial information is provided for informational purposes only and is not necessarily indicative of the operating results that would have occurred if the IPO and Reorganization Transactions or the due to the Secondary Transactions adjustments had been completed as of the dates set forth above, nor is it indicative of our future results. Additionally, the unaudited pro forma consolidated financial information does not give effect to the potential impact of any anticipated synergies, operating efficiencies, or cost savings that may result.

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UNAUDITED PRO FORMA CONSOLIDATED

STATEMENT OF OPERATIONS

See accompanying notes to unaudited pro forma financial information.

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UNAUDITED PRO FORMA CONSOLIDATED

STATEMENT OF OPERATIONS

See accompanying notes to unaudited pro forma financial information.

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Notes to Unaudited Pro Forma Statement of Operations

(Year Ended December 26, 2021 and Three Quarters ended September 25, 2022)

(1) Portillo’s Inc. is subject to U.S. federal income taxes, in addition to state and local taxes, with respect to its allocable share of any net taxable income of Portillo’s OpCo. The adjustment of $4.5 million to the income tax expense resulting from the IPO and Reorganization Transactions reflects our statutory tax rate of 27.9% applied to Portillo’s Inc.’s economic interest of 50.1% of Portillo’s OpCo following the IPO and Reorganization Transactions further applied to the portion of net income of Portillo’s OpCo that relates to pass-through entities whose income has not been previously subject to income tax expense for the period between December 28, 2020 and the date of the Company’s IPO.

(2) Following the consummation of the IPO and Reorganization Transactions, Portillo’s Inc. became the sole managing member of Portillo’s OpCo, and as sole managing member, the Company operates and controls all of the business and affairs of Portillo’s OpCo. As a result, Portillo’s Inc. consolidates the financial results of Portillo’s OpCo and reports a non-controlling interest representing the economic interest in Portillo’s OpCo held by the other members of Portillo’s OpCo. Following the IPO and Reorganization Transactions, we held approximately 50.1% of Portillo’s OpCo’s outstanding LLC Units, and the remaining LLC Units of Portillo’s OpCo would be held by the Continuing Pre-IPO LLC Members. Immediately following the IPO and Reorganization Transactions, the ownership percentage held by the noncontrolling interest was approximately 49.9%. Net income attributable to the noncontrolling interest represents approximately 49.9% of net income.

(3) Portillo’s Inc. is subject to U.S. federal income taxes, in addition to state and local taxes, with respect to its allocable share of any net taxable income of Portillo’s OpCo. For the year ended December 26, 2021 and the three quarters ended September 25, 2022, the pro forma adjustment of $0.5 million and $1.6 million, respectively, to the income tax expense resulting from the Secondary Transactions reflects our statutory tax rate of 27.9% applied to the additional economic interest in Portillo’s OpCo obtained in the Secondary Transactions applied to the portion of net income of Portillo’s OpCo that relates to pass-through entities whose income has not been previously subject to income tax expense.

(4) Following the Secondary Transactions, based on a weighted-average, we held approximately 66.7% of Portillo’s OpCo’s outstanding LLC Units, and the remaining LLC Units of Portillo’s OpCo are held by the Continuing Pre-IPO LLC Members. Immediately following the Secondary Transactions, based on a weighted-average, the ownership percentage held by the noncontrolling interest was approximately 33.3%. The pro forma adjustment reflects the reduction in the allocation of Portillo’s OpCo net income to the non-controlling interests. The weighted average ownership percentages for the applicable reporting periods are used to attribute net income to Portillo’s Inc. and the pre-IPO LLC Members.

(5) Pro forma basic net income per share of Class A common stock is computed by dividing the pro forma net income available to Class A common stockholders by the pro forma weighted-average shares of Class A common stock outstanding during the period. Pro forma diluted net income per share of Class A common stock is

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computed by dividing the pro forma net income available to Class A common stockholders by the pro forma weighted-average shares of Class A common stock outstanding to give effect to potentially dilutive securities.

Pro forma net income per share of Class B common stock is not presented because Class B common stock is not entitled to economic interests in Portillo’s Inc.

(6) Portillo’s OpCo used a portion of the proceeds from the issuance of LLC Units to Portillo’s Inc. in connection with the IPO and Reorganization Transactions to repay its Second Lien Term B-3 Loans. Our unpaid balance of our indebtedness on the Second Lien Term B-3 Loans, including unamortized debt discount and deferred issuance costs was $149.7 million bearing an effective interest at a rate of 11.83% as of December 28, 2020. We incurred a loss on extinguishment of debt of $8.4 million, consisting of $3.1 million for prepayment penalties and $5.3 million for the write-off of debt discount and deferred issuance costs. As such, interest expense will be reduced by $15.1 million as a result of the lower borrowings outstanding for the year ended December 26, 2021.

(7) Portillo’s OpCo used a portion of the proceeds from the issuance of LLC Units to Portillo’s Inc. in connection with the IPO to repay its redeemable preferred units in its entirety. As such, we have eliminated the preferred unit accretion for the year ended December 26, 2021.

(8) This adjustment represents the increase in compensation expense we would incur if the 1,794,195 performance stock options and 882,875 restricted stock units granted to certain employees and directors in connection with the IPO were granted on December 28, 2020 instead of on October 21, 2021 in connection with the IPO. This amount was calculated assuming the performance stock options and restricted stock units were granted on December 28, 2020 with the performance stock options having an exercise price equal to $20.00 per share, the initial public offering price of the shares of Class A common stock issued and sold in our IPO. The grant date fair values of the stock options were determined using a Monte Carlo simulation model.

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UNAUDITED PRO FORMA CONSOLIDATED BALANCE SHEET (AS OF SEPTEMBER 25, 2022)

See accompanying notes to unaudited pro forma financial information.

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Notes to Unaudited Pro Forma Consolidated Balance Sheet (as of September 25, 2022)

(1) Reflects the receipt of proceeds from the November Secondary Offering of $181.5 million, based on the sale of 8,000,000 shares of Class A common stock at a public offering price of $22.69 per share of common stock, excluding the exercise by the underwriters of their option to purchase additional shares of common stock.

The proceeds from November Secondary Offering were used for the following (in thousands):

(2) We are subject to U.S. federal, state and local income taxes and will file income tax returns for U.S. federal and certain state and local jurisdictions. This adjustment reflects the recognition of deferred taxes in connection with the Reorganization Transaction assuming the federal rates currently in effect and the highest statutory rates apportioned to each state and local jurisdiction.

We have recorded a pro forma deferred tax asset adjustment of $43.9 million (assuming that the underwriters do not exercise their option to purchase additional shares of Class A common stock).

(3) We estimate $1.1 million of additional offering costs will have been incurred in connection with the November Secondary Offering. Offering costs will be expensed as incurred.

(4) In connection with the IPO and Reorganization Transactions, we became a party to a Tax Receivable Agreement with the TRA Parties. Under the Tax Receivable Agreement, we generally will be required to pay 85% of the applicable cash savings, if any, in U.S. federal, state and local income tax that we actually realize as a result of (i) our allocable share of existing tax basis in depreciable or amortizable assets relating to LLC Units acquired in the IPO, (ii) certain favorable tax attributes we acquired from the Blocker Companies in the Mergers, (iii) increases in our allocable share of then existing tax basis in depreciable or amortizable assets, and adjustments to the tax basis of the tangible and intangible assets, of Portillo’s OpCo and its subsidiaries, as a result of (x) sales or exchanges of interests in Portillo’s OpCo in connection with the IPO and (y) subsequent redemptions or exchanges of LLC Units by Continuing Pre-IPO LLC Members for cash or Class A common stock, including in connection with this offering, and (iv) certain other tax benefits related to entering into the Tax Receivable Agreement, including payments made under the Tax Receivable Agreement.

The net deferred tax asset adjustment of $43.9 million, resulting from the November Secondary Offering, and the $50.4 million adjustment related to the Tax Receivable Agreement liability are assuming: (i) only exchanges associated with the November Secondary Offering, (ii) a share price equal to $22.69, (iii) an estimated statutory tax rate of 27.9%, (iv) we will have sufficient taxable income to fully utilize the tax benefits, (v) no material changes in tax law and (vi) future Tax Receivable Agreement payments.

The net impact of the adjustments to net deferred taxes and the Tax Receivable Agreement liability of $6.5 million has been recorded as a decrease to additional paid-in capital, as these adjustments arise from equity transactions of the Company.

If all of the Continuing Pre-IPO LLC Members were to exchange their Portillo’s OpCo units, we would recognize a total liability of approximately $459.6 million, which would be inclusive of the existing tax receivable liability and the incremental liability associated with the exchange of the Continuing Pre-IPO LLC Members, assuming (i) that the Continuing Pre-IPO LLC Members exchanged all of their Portillo’s OpCo units immediately after the completion of the November Secondary Offering at a public offering price of $22.69 per share, (ii) no material changes in relevant tax law, (iii) that we have sufficient taxable income in each year to

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realize on a current basis the increased depreciation, amortization and other tax benefits that are the subject of the Tax Receivable Agreement and (iv) the underwriters’ option to purchase additional shares of Class A common stock was not exercised.

These amounts are estimates and have been prepared for informational purposes only. The actual amount of deferred tax assets and related liabilities that we will recognize will differ based on, among other things, the timing of the exchanges, the price of shares of our Class A common stock at the time of the exchange and the tax rates then in effect.

(5) Assuming completion of the November Secondary Offering as of September 25, 2022 (and no exercise of the underwriters’ option to purchase additional shares of Class A common stock, if any), we would have held 48,118,623 LLC Units, constituting 66.9% of the outstanding economic interests in Portillo’s OpCo.

The following table is a reconciliation of the November Secondary Offering adjustments impacting non-controlling interest (in thousands):

(6) The following table is a reconciliation of the November Secondary Offering adjustments impacting Class A common stock:

(7) Represents an adjustment to stockholders’ equity reflecting (i) par value of $0.01 for Class A common stock and $0.00001 for Class B common stock to be outstanding following the November Secondary Offering and (ii) an increase of $43.4 million to allocate a portion of Portillo’s Inc.’s equity to the non-controlling interests, which is calculated as approximately 33.1% of total Stockholders’ equity as of September 25, 2022, as described in Note 5. The reconciliations below assume that the underwriters’ option to purchase additional shares of Class A common stock was not exercised.

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The following table is a reconciliation of the November Secondary Offering adjustments impacting additional paid-in-capital (in thousands):

(8) The following table is a reconciliation of the November Secondary Offering adjustments impacting retained earnings (accumulated deficit) (in thousands):

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES TO NON-U.S. HOLDERS

The following is a summary of certain material U.S. federal income tax consequences of the purchase, ownership and disposition of shares of our Class A common stock as of the date hereof. Except where noted, this summary deals only with Class A common stock that is held as a capital asset by a non-U.S. holder (as defined below).

A “non-U.S. holder” means a beneficial owner of shares of our Class A common stock (other than an entity treated as a partnership for U.S. federal income tax purposes) that is not, for U.S. federal income tax purposes, any of the following:

This summary is based upon provisions of the Internal Revenue Code of 1986, as amended (the “Code”), and regulations, rulings and judicial decisions as of the date hereof. Those authorities may be changed, perhaps retroactively, so as to result in U.S. federal income tax consequences different from those summarized below. This summary does not address all aspects of U.S. federal income taxes and does not deal with other U.S. federal taxes or with foreign, state, local or other tax considerations that may be relevant to non-U.S. holders in light of their particular circumstances. In addition, it does not represent a detailed description of the U.S. federal income tax consequences applicable to you if you are subject to special treatment under the U.S. federal income tax laws (including if you are a U.S. expatriate, foreign pension fund, “controlled foreign corporation,” “passive foreign investment company” or a partnership or other pass-through entity for U.S. federal income tax purposes). We cannot assure you that a change in law will not alter significantly the tax considerations that we describe in this summary.

If a partnership (or other entity treated as a partnership for U.S. federal income tax purposes) holds shares of our Class A common stock, the tax treatment of a partner will generally depend upon the status of the partner and the activities of the partnership. If you are a partner of a partnership holding our Class A common stock, you should consult your tax advisors.

If you are considering the purchase of our Class A common stock, you should consult your own tax advisors concerning the particular U.S. federal income tax consequences to you of the purchase, ownership and disposition of our Class A common stock, as well as the consequences to you arising under other U.S. federal tax laws and the laws of any other taxing jurisdiction.

Dividends

In the event that we make a distribution of cash or other property (other than certain pro rata distributions of our Class A common stock) in respect of shares of our Class A common stock, the distribution generally will be treated as a dividend for U.S. federal income tax purposes to the extent it is paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Any portion of a distribution that exceeds our current and accumulated earnings and profits generally will be treated first as a tax-free return of capital, causing a reduction in the adjusted tax basis of a non-U.S. holder’s Class A common stock, and to the extent the amount of the distribution exceeds a non-U.S. holder’s adjusted tax basis in shares of our Class A common stock, the excess will be treated as gain from the disposition of shares of our Class A common stock

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(the tax treatment of which is discussed below under “—Gain on Disposition of Class A Common Stock”). Dividends paid to a non-U.S. holder generally will be subject to withholding of U.S. federal income tax at a 30% rate or such lower rate as may be specified by an applicable income tax treaty, subject to the discussion of FATCA below under “—Additional Withholding Requirements.” However, dividends that are effectively connected with the conduct of a trade or business by the non-U.S. holder within the United States (and, if required by an applicable income tax treaty, are attributable to a U.S. permanent establishment) are not subject to the withholding tax, provided certain certification and disclosure requirements are satisfied. Instead, such dividends are subject to U.S. federal income tax on a net income basis in the same manner as if the non-U.S. holder were a U.S. person as defined under the Code. Any such effectively connected dividends received by a foreign corporation may be subject to an additional “branch profits tax” at a 30% rate or such lower rate as may be specified by an applicable income tax treaty.

A non-U.S. holder who wishes to claim the benefit of an applicable treaty rate and avoid backup withholding, as discussed below, for dividends will be required (a) to provide the applicable withholding agent with a properly executed IRS Form W-8BEN or Form W-8BEN-E (or other applicable form) certifying under penalty of perjury that such holder is not a U.S. person as defined under the Code and is eligible for treaty benefits or (b) if our Class A common stock is held through certain foreign intermediaries, to satisfy the relevant certification requirements of applicable U.S. Treasury regulations. Special certification and other requirements apply to certain non-U.S. holders that are pass-through entities rather than corporations or individuals.

A non-U.S. holder eligible for a reduced rate of U.S. federal withholding tax pursuant to an income tax treaty may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS.

Gain on Disposition of Class A Common Stock

Subject to the discussion of backup withholding below, any gain realized by a non-U.S. holder on the sale or other disposition of our Class A common stock generally will not be subject to U.S. federal income tax unless:

A non-U.S. holder described in the first bullet point immediately above will be subject to tax on the gain derived from the sale or other disposition in the same manner as if the non-U.S. holder were a U.S. person as defined under the Code. In addition, if any non-U.S. holder described in the first bullet point immediately above is a foreign corporation, the gain realized by such non-U.S. holder may be subject to an additional “branch profits tax” at a 30% rate or such lower rate as may be specified by an applicable income tax treaty. An individual non-U.S. holder described in the second bullet point immediately above will be subject to a 30% (or such lower rate as may be specified by an applicable income tax treaty) tax on the gain derived from the sale or other disposition, which gain may be offset by U.S. source capital losses even though the individual is not considered a resident of the United States, provided the non-U.S. holder has timely filed U.S. federal income tax returns with respect to such losses.

Generally, a corporation is a “U.S. real property holding corporation” if the fair market value of its U.S. real property interests equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests and its other assets used or held for use in a trade or business (all as determined for U.S. federal income tax purposes). We believe we are not and do not anticipate becoming a “U.S. real property holding corporation” for U.S. federal income tax purposes.

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Information Reporting and Backup Withholding

Distributions paid to a non-U.S. holder and the amount of any tax withheld with respect to such distributions generally will be reported to the IRS. Copies of the information returns reporting such distributions and any withholding may also be made available to the tax authorities in the country in which the non-U.S. holder resides under the provisions of an applicable income tax treaty.

A non-U.S. holder will not be subject to backup withholding on dividends received if such holder certifies under penalty of perjury that it is a non-U.S. holder (and the payor does not have actual knowledge or reason to know that such holder is a U.S. person as defined under the Code), or such holder otherwise establishes an exemption.

Information reporting and, depending on the circumstances, backup withholding will apply to the proceeds of a sale or other disposition of our Class A common stock made within the United States or conducted through certain U.S.-related financial intermediaries, unless the beneficial owner certifies under penalty of perjury that it is a non-U.S. holder (and the payor does not have actual knowledge or reason to know that the beneficial owner is a U.S. person as defined under the Code), or such owner otherwise establishes an exemption.

Backup withholding is not an additional tax and any amounts withheld under the backup withholding rules will be allowed as a refund or a credit against a non-U.S. holder’s U.S. federal income tax liability provided the required information is timely furnished to the IRS.

Additional Withholding Requirements

Under Sections 1471 through 1474 of the Code (such Sections commonly referred to as FATCA), a 30% U.S. federal withholding tax may apply to any dividends paid on our Class A common stock to (i) a “foreign financial institution” (as specifically defined in the Code) which does not provide sufficient documentation, typically on IRS Form W-8BEN-E, evidencing either (x) an exemption from FATCA or (y) its compliance (or deemed compliance) with FATCA (which may alternatively be in the form of compliance with an intergovernmental agreement with the United States) in a manner which avoids withholding, or (ii) a “non-financial foreign entity” (as specifically defined in the Code) which does not provide sufficient documentation, typically on IRS Form W-8BEN-E, evidencing either (x) an exemption from FATCA or (y) adequate information regarding certain substantial U.S. beneficial owners of such entity (if any). Under proposed U.S. Treasury regulations promulgated by the Treasury Department on December 13, 2018, which state that taxpayers may rely on the proposed Treasury regulations until final Treasury regulations are issued, this withholding tax will not apply to the gross proceeds from the sale or disposition of our Class A common stock. An intergovernmental agreement between the United States and an applicable foreign country may modify these requirements. If a dividend payment is both subject to withholding under FATCA and subject to the withholding tax discussed above under “—Dividends,” the withholding under FATCA may be credited against, and therefore reduce, such other withholding tax. You should consult your own tax advisors regarding these requirements and whether they may be relevant to your ownership and disposition of our Class A common stock.

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UNDERWRITING

BofA Securities, Inc. and Jefferies LLC are acting as the underwriters for this offering.

Under the terms and subject to the conditions contained in an underwriting agreement dated as of the date of this prospectus supplement, we have agreed to sell to the underwriters named below, and the underwriters have agreed to purchase from us, severally and not jointly, the number of shares of Class A common stock set forth opposite its name below:

The underwriting agreement provides that the obligations of the underwriters are subject to certain conditions precedent such as the receipt of officers’ certificates and legal opinions and approval of certain legal matters by their counsel. The underwriting agreement provides that the underwriters will purchase all of the shares of Class A common stock if any of them are purchased. We have agreed to indemnify the underwriters and certain of their controlling persons against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters have advised us that, following the completion of this offering, they currently intend to make a market in the Class A common stock as permitted by applicable laws and regulations. However, the underwriters are not obligated to do so, and the underwriters may discontinue any market-making activities at any time without notice in their sole discretion. Accordingly, no assurance can be given as to the liquidity of the trading market for the Class A common stock, that you will be able to sell any of the common stock held by you at a particular time or that the prices that you receive when you sell will be favorable.

The underwriters are offering the shares of Class A common stock subject to their acceptance of the shares of Class A common stock from us and subject to prior sale. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commission and Expenses

The underwriters are purchasing the shares of Class A common stock from the Company at $22.69 per share (representing $181,520,000 aggregate proceeds, before expenses). The underwriters may offer the shares of common stock from time to time for sale in one or more transactions on the Nasdaq, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices. The underwriters may effect such transactions by selling shares of Class A common stock to or through dealers, and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or purchasers of shares of Class A common stock for whom it may act as agents or to whom it may sell as principal. The difference between the price at which the underwriters purchase shares and the price at which the underwriters resell such shares may be deemed underwriting compensation.

We estimate expenses payable by us in connection with this offering will be approximately $1,100,000. We have agreed to reimburse the underwriters for certain of their expenses in an amount up to $30,000.

Listing

Our common stock is listed on the Nasdaq under the trading symbol “PTLO.”

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Stamp Taxes

If you purchase shares of Class A common stock offered in this prospectus supplement, you may be required to pay stamp taxes and other charges under the laws and practices of the country of purchase, in addition to the offering price listed on the cover page of this prospectus supplement.

Option to Purchase Additional Shares

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus supplement, to purchase, from time to time, in whole or in part, up to an aggregate of 1,200,000 shares of Class A common stock from us at the purchase price set forth on the cover page of this prospectus supplement. If the underwriters exercise this option, each underwriter will be obligated, subject to specified conditions, to purchase a number of additional shares of Class A common stock proportionate to that underwriter’s initial purchase commitment as indicated in the table above.

No Sales of Similar Securities

In connection with this offering, our executive officers and directors and the selling stockholders in this offering have agreed that, for a period of 30 days from the date of this prospectus supplement (the “lock-up period”), they will not, without the prior written consent of the underwriters, dispose of or hedge any shares of our common stock or any securities convertible into or exchangeable for our common stock (including LLC Units and options for shares of our Class A common stock) subject to certain exceptions noted below.

During the lock-up period, we and our officers, directors and certain Pre-IPO LLC Members and Reorganization Parties have agreed not to directly or indirectly, without the prior written consent of the underwriters:

The foregoing lock-up restrictions will not apply to the registration of the offer and sale of shares of Class A common stock, the sale of shares of Class A common stock to the underwriters, the sale of the stockholder’s LLC Units, shares of Class A common stock or other Related Securities to us or any of our subsidiaries in connection with the purchase of LLC Units from the stockholder by us or any of our subsidiaries with the net proceeds of this offering, and any exchange, transfer or sale as contemplated by this prospectus supplement. In addition, the foregoing lock-up restrictions shall not apply to the transfer of shares of Class A common stock or Related Securities:

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provided, that in the case of any transfer pursuant to the first through seventh bullets above, such transfer shall not involve a disposition for value and each donee, devisee, transferee or distributee shall execute and deliver a written agreement accepting the restrictions set forth in the preceding paragraph; provided further that in the case of any transfer pursuant to the first, and third through eleventh bullets above, it shall be a condition to such transfer that no public filing, report or announcement shall be voluntarily made and if any filing under Section 16(a) of the Exchange Act or other public filing, report or announcement reporting a reduction in beneficial ownership of shares of Class A common stock or Related Securities in connection with such transfer or distribution shall be legally required during the lock-up period, such filing, report or announcement shall clearly indicate in the footnotes thereto the nature and conditions of such transfer.

The underwriters may, in their sole discretion and at any time or from time to time before the termination of the lock-up period release all or any portion of the securities subject to lock-up agreements. There are no existing agreements between the underwriters and any of our shareholders who will execute a lock-up agreement, providing consent to the sale of shares prior to the expiration of the lock-up period.

Stabilization

The underwriters have advised us that, pursuant to Regulation M under the Exchange Act, certain persons participating in the offering may engage in short sale transactions, stabilizing transactions, syndicate covering transactions or the imposition of penalty bids in connection with this offering. These activities may have the effect of stabilizing or maintaining the market price of the common stock at a level above that which might otherwise prevail in the open market. Establishing short sales positions may involve either “covered” short sales or “naked” short sales.

“Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares of our common stock in this offering. The underwriters may close out any covered short position by either exercising their option to purchase additional shares of our common stock or purchasing shares of our common stock in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the option to purchase additional shares.

“Naked” short sales are sales in excess of the option to purchase additional shares of our common stock. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the shares of our common stock in the open market after pricing that could adversely affect investors who purchase in this offering.

A stabilizing bid is a bid for the purchase of shares of common stock on behalf of the underwriters for the purpose of fixing or maintaining the price of the common stock. A syndicate covering transaction is the bid for or the purchase of shares of common stock on behalf of the underwriters to reduce a short position incurred by the underwriters in connection with the offering. Similar to other purchase transactions, the underwriter’s purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. A penalty bid is an arrangement permitting the underwriters to reclaim the selling concession otherwise accruing to a syndicate member in connection with the offering if the common stock originally sold by such syndicate member are purchased in a syndicate covering transaction and therefore have not been effectively placed by such syndicate member.

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Neither we, nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common stock. The underwriters are not obligated to engage in these activities and, if commenced, any of the activities may be discontinued at any time.

Electronic Distribution

A prospectus in electronic format may be made available by e-mail or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may agree with us to allocate a specific number of shares of common stock for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus in electronic format, the information on the underwriters’ web sites and any information contained in any other web site maintained by any of the underwriters is not part of this prospectus supplement, has not been approved and/or endorsed by us or the underwriters and should not be relied upon by investors.

Other Activities and Relationships

The underwriters and certain of their affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and certain of their affiliates have, from time to time, performed, and may in the future perform, various commercial and investment banking and financial advisory services for us and our affiliates, for which they received or will receive customary fees and expenses, including acting as underwriters for our securities offerings.

In the ordinary course of their various business activities, the underwriters and certain of their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments issued by us and our affiliates. If the underwriters or their respective affiliates have a lending relationship with us, they routinely hedge their credit exposure to us consistent with their customary risk management policies. The underwriters and their respective affiliates may hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities or the securities of our affiliates, including potentially the common stock offered hereby. Any such short positions could adversely affect future trading prices of the common stock offered hereby. The underwriters and certain of their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments. In addition, certain of the underwriters and/or their affiliates are lenders under our First Lien Credit Facilities.

Selling Restrictions

Canada

Resale Restrictions

The distribution of the shares in Canada is being made only in the provinces of Ontario, Quebec, Alberta, British Columbia, Manitoba, New Brunswick and Nova Scotia on a private placement basis exempt from the requirement that we prepare and file a prospectus with the securities regulatory authorities in each province where trades of these shares are made. Any resale of the shares in Canada must be made under applicable securities laws which may vary depending on the relevant jurisdiction, and which may require resales to be made

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under available statutory exemptions or under a discretionary exemption granted by the applicable Canadian securities regulatory authority. Purchasers are advised to seek legal advice prior to any resale of the shares.

Representations of Canadian Purchasers

By purchasing shares in Canada and accepting delivery of a purchase confirmation, a purchaser is representing to us and the dealer from whom the purchase confirmation is received that:

Conflicts of Interest

Canadian purchasers are hereby notified that certain of the underwriters are relying on the exemption set out in section 3A.3 or 3A.4, if applicable, of National Instrument 33-105—Underwriting Conflicts from having to provide certain conflict of interest disclosure in this document.

Statutory Rights of Action

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if the prospectus (including any amendment thereto) such as this document contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser of these shares in Canada should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Enforcement of Legal Rights

All of our directors and officers as well as the experts named herein may be located outside of Canada and, as a result, it may not be possible for Canadian purchasers to effect service of process within Canada upon us or those persons. All or a substantial portion of our assets and the assets of those persons may be located outside of Canada and, as a result, it may not be possible to satisfy a judgment against us or those persons in Canada or to enforce a judgment obtained in Canadian courts against us or those persons outside of Canada.

Taxation and Eligibility for Investment

Canadian purchasers of shares should consult their own legal and tax advisors with respect to the tax consequences of an investment in the share in their particular circumstances and about the eligibility of the shares for investment by the purchaser under relevant Canadian legislation.

Australia

This prospectus supplement is not a disclosure document for the purposes of Australia’s Corporations Act 2001 (Cth) of Australia, or Corporations Act, has not been lodged with the Australian Securities & Investments Commission and is only directed to the categories of exempt persons set out below. Accordingly, if you receive this prospectus supplement in Australia:

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You confirm and warrant that you are either:

To the extent that you are unable to confirm or warrant that you are an exempt sophisticated investor, associated person or professional investor under the Corporations Act any offer made to you under this prospectus supplement is void and incapable of acceptance.

You warrant and agree that you will not offer any of the shares issued to you pursuant to this prospectus supplement for resale in Australia within 12 months of those shares being issued unless any such resale offer is exempt from the requirement to issue a disclosure document under section 708 of the Corporations Act.

European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant State”), no shares have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the shares which have been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the shares may be offered to the public in that Relevant State at any time:

provided that no such offer of the shares shall require us or any of the representatives to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of this provision, the expression “offer to the public” in relation to the shares in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

Hong Kong

No shares have been offered or sold, and no shares may be offered or sold, in Hong Kong, by means of any document, other than to persons whose ordinary business is to buy or sell shares or debentures, whether as principal or agent; or to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong (“SFO”) and any rules made under that Ordinance; or in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong (“CO”) or which do not constitute an offer or invitation to the public for the purpose of the CO or the SFO. No document, invitation or advertisement relating to the shares has been issued or may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or

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the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted under the securities laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the SFO and any rules made under that Ordinance.

This prospectus supplement has not been registered with the Registrar of Companies in Hong Kong. Accordingly, this prospectus supplement may not be issued, circulated or distributed in Hong Kong, and the shares may not be offered for subscription to members of the public in Hong Kong. Each person acquiring the shares will be required, and is deemed by the acquisition of the shares, to confirm that he is aware of the restriction on offers of the shares described in this prospectus supplement and the relevant offering documents and that he is not acquiring, and has not been offered any shares in circumstances that contravene any such restrictions.

Israel

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968, or the Securities Law, and has not been filed with or approved by the Israel Securities Authority. In Israel, this prospectus supplement is being distributed only to, and is directed only at, and any offer of the shares is directed only at, (i) a limited number of persons in accordance with the Israeli Securities Law and (ii) investors listed in the first addendum, or the Addendum, to the Israeli Securities Law, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange, underwriters, venture capital funds, entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case, purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors are required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

Japan

The offering has not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948 of Japan, as amended), or FIEL, and the underwriters will not offer or sell any shares, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the FIEL and any other applicable laws, regulations and ministerial guidelines of Japan.

Singapore

This prospectus supplement has not been and will not be lodged or registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

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Switzerland

The shares may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange (“SIX”) or on any other stock exchange or regulated trading facility in Switzerland. This prospectus supplement has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this prospectus supplement nor any other offering or marketing material relating to the shares or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this prospectus supplement nor any other offering or marketing material relating to the offering, the Company or the shares have been or will be filed with or approved by any Swiss regulatory authority. In particular, this prospectus supplement will not be filed with, and the offer of shares will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA, and the offer of shares has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes (“CISA”). The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of shares.

United Kingdom

No shares have been offered or will be offered pursuant to the offering to the public in the United Kingdom prior to the publication of a prospectus in relation to the shares which has been approved by the Financial Conduct Authority, except that the shares may be offered to the public in the United Kingdom at any time:

provided that no such offer of the shares shall require the Company or any Manager to publish a prospectus pursuant to Section 85 of the FSMA or supplement a prospectus pursuant to Article 23 of the UK Prospectus Regulation. For the purposes of this provision, the expression an “offer to the public” in relation to the shares in the United Kingdom means the communication in any form and by any means of sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares and the expression “UK Prospectus Regulation” means Regulation (EU) 2017/1129 as it forms part of domestic law by virtue of the European Union (Withdrawal) Act 2018.

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WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION OF DOCUMENTS BY REFERENCE

We file annual, quarterly and current reports, proxy statements and other information with the SEC. The SEC maintains an Internet site that contains our reports, proxy and other information regarding us and other issuers that file electronically with the SEC, at http://www.sec.gov. Our SEC filings are also available free of charge at our website (www.portillos.com). However, except for our filings with the SEC that are incorporated by reference into this prospectus supplement, the information on our website is not, and should not be deemed to be, a part of, or incorporated by reference into this prospectus supplement.

The SEC allows “incorporation by reference” into this prospectus supplement of information that we file with the SEC. This permits us to disclose important information to you by referencing these filed documents. Any information referenced this way is considered to be a part of this prospectus supplement and any information filed by us with the SEC subsequent to the date of this prospectus supplement automatically will be deemed to update and supersede this information. We incorporate by reference the following documents which we have filed with the SEC (excluding any documents or portions of such documents that have been “furnished” but not “filed” for purposes of the Exchange Act):

We incorporate by reference any filings made by us with the SEC in accordance with Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date of this prospectus supplement and the date all of the securities offered hereby are sold or the offering is otherwise terminated, with the exception of any information furnished under Item 2.02 and Item 7.01 (including any financial statements or exhibits relating thereto furnished pursuant to Item 9.01) of Form 8-K, which is not deemed filed and which is not incorporated by reference herein. Any such filings shall be deemed to be incorporated by reference and to be a part of this prospectus supplement from the respective dates of filing of those documents.

This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the SEC and do not contain all of the information in the registration statement. The full registration statement may be obtained from the SEC or us, as provided below. Statements in this prospectus supplement, the accompanying prospectus or free writing prospectus about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement at the SEC’s website, as provided above.

Any statement contained in a document incorporated or deemed to be incorporated by reference in this prospectus supplement or the accompanying prospectus will be deemed to be modified or superseded to the extent that a statement contained herein or in any other subsequently filed document which also is or is deemed to be incorporated by reference in this prospectus supplement modifies or supersedes that statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

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We will provide to each person, including any beneficial owner, to whom a prospectus supplement is delivered, without charge, upon written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus supplement but not delivered with this prospectus supplement, excluding any exhibits to those documents unless the exhibit is specifically incorporated by reference as an exhibit in this prospectus supplement. You should direct requests for documents to:

Portillo’s Inc.

2001 Spring Road, Suite 400

Oak Brook, Illinois 60523

(630) 954-3773

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LEGAL MATTERS

Weil, Gotshal & Manges LLP, New York, New York, has passed upon the validity of the Class A common stock offered hereby on behalf of us. Certain legal matters will be passed upon on behalf of the underwriters by Latham  & Watkins LLP.

EXPERTS

The financial statements of Portillo’s Inc., incorporated by reference in this Prospectus, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

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PROSPECTUS

Portillo’s Inc.

Class A Common Stock

Preferred Stock

We may offer and sell, from time to time in one or more offerings, shares of our Class A common stock, par value $0.01 (the “Class A common stock”) and preferred stock in amounts, at prices and on terms determined at the time of offering. This prospectus describes some of the general terms of these securities and the general manner in which these securities will be offered. Each time securities are offered pursuant to this prospectus, we will file a prospectus supplement and attach it to this prospectus. We also may provide investors with a free writing prospectus. The prospectus supplement or any free writing prospectus will contain more specific information about the offering and, if applicable, prices and terms of the securities. Such supplements or free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus and the applicable prospectus supplement or free writing prospectus, as well as the documents incorporated by reference herein or therein, before you invest in any of our securities.

In addition, the selling stockholders to be named in a supplement to this prospectus may from time to time offer or sell one or more of the securities registered herein. To the extent that any selling stockholders resell any securities, the selling stockholders may be required to provide you with this prospectus and a prospectus supplement identifying and containing specific information about the selling stockholders and the amount and terms of the securities being offered. We will not receive any proceeds from the sale of securities by the selling stockholders.

This prospectus may not be used to offer and sell shares of our securities unless accompanied by a prospectus supplement or a free writing prospectus.

The securities may be sold at fixed prices, prevailing market prices at the times of sale, prices related to the prevailing market prices and varying prices determined at the times of sale or negotiated prices. The securities offered by this prospectus and the accompanying prospectus supplement or free writing prospectus may be offered by us or the selling stockholders directly to investors or to or through underwriters, dealers or other agents. The prospectus supplement for each offering will describe in detail the plan of distribution for that offering and will set forth the names of any underwriters, dealers or agents involved in the offering and any applicable fees, commissions or discount arrangements.

Our Class A common stock is listed on Nasdaq Global Select Market (“Nasdaq”) under the symbol “PTLO.” Each prospectus supplement will indicate whether the securities offered thereby will be listed on any securities exchange. On November 11, 2022, the last reported sale price of our Class A common stock was $25.41 per share.

We are a holding company and our principal asset is a controlling equity interest in PHD Group Holdings LLC. We are the sole managing member of PHD Group Holdings LLC. We operate and control all of the business and affairs of PHD Group Holdings LLC and, through PHD Group Holdings LLC and its subsidiaries, conduct our business.

Investing in our securities involves risks. You should carefully read and consider the risk factors included in this prospectus, in our periodic reports, in any applicable prospectus supplement relating to a specific offering of securities and in any other documents we file with the Securities and Exchange Commission (“SEC”). See the sections entitled “Risk Factors” below on page 6, in our other filings with the Securities and Exchange Commission and in the applicable prospectus supplement, if any.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is November 14, 2022.

TABLE OF CONTENTS

i

ABOUT THIS PROSPECTUS

This prospectus is part of an automatic shelf registration statement on Form S-3 that we filed with the SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”). Under the automatic shelf registration process, we or the selling stockholders to be named in a prospectus supplement or free writing prospectus may offer and sell, from time to time, in one or more offerings, the securities described in this prospectus. This prospectus provides you with a general description of our securities that we may offer. To the extent required by applicable law, each time we or the selling stockholders sell securities, we will provide you with this prospectus and, to the extent required, a prospectus supplement that will contain more information about the specific terms of the offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. Each such prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you), if any, may also add, update or change information contained in this prospectus or in documents incorporated by reference into this prospectus. We urge you to carefully read this prospectus, any applicable prospectus supplement, if any, and any related free writing prospectus, together with the information incorporated herein and therein by reference as described under the headings “Where You Can Find Additional Information; Incorporation of Documents by Reference” before buying any of our securities being offered. If there is any inconsistency between the information in this prospectus and any prospectus supplement or free writing prospectus, you should rely on the information provided in the prospectus supplement or free writing prospectus, as applicable.

You should rely only on the information contained in this prospectus, and any accompanying prospectus supplement, including the information incorporated by reference herein as described under “Where You Can Find More Information; Incorporation of Documents by Reference,” and any free writing prospectus that we prepare and distribute.

Neither we nor the selling stockholders or any of their respective affiliates have authorized anyone to provide you with information other than that contained in or incorporated by reference into this prospectus, any accompanying prospectus supplement or any free writing prospectus related hereto that we may authorize to be delivered to you. If given or made, any such other information or representation should not be relied upon as having been authorized by us or any selling stockholders. We and the selling stockholders may only offer to sell, and seek offers to buy any securities in jurisdictions where offers and sales are permitted.

This prospectus and any accompanying prospectus supplement or other offering materials do not contain all of the information included in the registration statement as permitted by the rules and regulations of the SEC. For further information, we refer you to the registration statement on Form S-3, including its exhibits. We are subject to the informational requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and, therefore, file reports and other information with the SEC. Statements contained in this prospectus and any accompanying prospectus supplement or other offering materials about the provisions or contents of any agreement or other document are only summaries. If SEC rules require that any agreement or document be filed as an exhibit to the registration statement, you should refer to that agreement or document for its complete contents.

You should assume that the information in this prospectus, any accompanying prospectus supplement or any other offering materials is only accurate as of the date on its respective cover, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, unless otherwise indicated. Our business, financial condition, results of operations and prospects may have changed since such date.

THIS PROSPECTUS MAY NOT BE USED TO SELL ANY SHARES OF OUR SECURITIES UNLESS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT OR A FREE WRITING PROSPECTUS.

1

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Certain statements made in this prospectus, the documents that are incorporated by reference in this prospectus and other written or oral statements made by or on behalf of Portillo’s may constitute “forward-looking statements” within the meaning of the “safe harbor” provisions of the United States Private Securities Litigation Reform Act of 1995 which are subject to known and unknown risks, uncertainties and other important factors that may cause actual results to be materially different from the statements made herein. All statements other than statements of historical fact are forward-looking statements. You can identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. These statements may include words such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “future,” “outlook,” “potential,” “project,” “projection,” “plan,” “intend,” “seek,” “may,” “could,” “would,” “will,” “should,” “can,” “can have,” “likely,” the negatives thereof and other similar expressions. These forward-looking statements are based only on our current beliefs, expectations and assumptions regarding the future of our business, future plans and strategies, projections, anticipated events and trends, the economy and other future conditions and speak only as of the date on which it is made. Many of the forward-looking statements are located in “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” which may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to, the following:

2

This list of factors that may affect future performance and the accuracy of forward-looking statements is illustrative but not exhaustive. In addition, new risks and uncertainties may arise from time to time. Accordingly, all forward-looking statements should be evaluated with an understanding of their inherent uncertainty and we caution accordingly against relying on forward-looking statements.

Consider these factors carefully in evaluating the forward-looking statements. For further information about these and other risks and uncertainties as well as strategic initiatives, see “Risk Factors” in our most recent annual report on Form 10-K and subsequent reports filed by us with the SEC, including on Form 8-K.

All subsequent written and oral forward-looking statements attributable to us or persons acting on our behalf are expressly qualified in their entirety by these cautionary statements. The forward-looking statements included herein are made only as of the date hereof, and we do not undertake any obligation to release publicly any revisions to such forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

BASIS OF PRESENTATION

As used in this prospectus, unless otherwise noted or the context requires otherwise:

3

TRADEMARKS

We own or have the rights to use various trademarks, trade names and service marks, including “Portillo’s” and various logos used in association with our name. Solely for convenience, any trademarks, trade names, service marks or copyrights referred to or used herein are listed without the applicable ^©, ^® or ^™ symbol, but such references or uses are not intended to indicate, in any way, that we, or the applicable owner, will not assert, to the fullest extent under applicable law, our or their, as applicable, rights to these trademarks, trade names, service marks and copyrights. Other trademarks, trade names, service marks or copyrights of any other company appearing in this prospectus are, to our knowledge, the property of their respective owners.

4

THE COMPANY

Portillo’s serves iconic Chicago street food through high-energy, multichannel restaurants designed to ignite the senses and create a memorable dining experience. Since our founding in 1963 in a small trailer which Dick Portillo called “The Dog House,” Portillo’s has grown to become a treasured brand with a passionate (some might say obsessed) nationwide following. Our diverse menu features all-American favorites such as Chicago-style hot dogs and sausages, Italian beef sandwiches, chopped salads, burgers, crinkle-cut french fries, homemade chocolate cake and milkshakes. We create a consumer experience like no other by combining the best attributes of fast casual and quick service concepts with an exciting energy-filled atmosphere and restaurant model capable of generating tremendous volumes.

Portillo’s Inc. was incorporated in Delaware on June 8, 2021. Our principal executive offices are located at 2001 Spring Road, Suite 400, Oak Brook, IL 60523, and our telephone number is (630) 954-3773. Our corporate website address is www.portillos.com. Our corporate website and the information contained on, or that can be accessed through, the website is not deemed to be incorporated by reference in, and is not considered part of, this prospectus. You should not rely on any such information in making your decision whether to purchase our securities.

5

RISK FACTORS

Investing in our securities involves risks. You should carefully consider the risk factors described under the heading “Risk Factors” in our most recent annual report on Form 10-K and any updates to those risk factors or new risk factors contained in our subsequent quarterly reports on Form 10-Q and current reports on Form 8-K, all of which are incorporated by reference into this prospectus, as the same may be amended, supplemented or superseded from time to time by our filings under the Exchange Act, as well as any prospectus supplement relating to a specific offering or resale. Before making any investment decision, you should carefully consider these risks as well as other information we include or incorporate by reference in this prospectus or in any applicable prospectus supplement or free writing prospectus. For more information, see the section entitled “Where You Can Find More Information; Incorporation of Documents by Reference” in this prospectus. These risks could materially affect our business, results of operations or financial condition and affect the value of our securities. You could lose all or part of your investment. Additionally, the risks and uncertainties discussed in this prospectus or in any document incorporated by reference into this prospectus are not the only risks and uncertainties that we face, and additional risks and uncertainties not presently known to us or that we currently deem immaterial may also affect our business, results of operations or financial condition.

6

USE OF PROCEEDS

We intend to use the net proceeds from the sale of the securities as set forth in any applicable prospectus supplement. We will not receive any proceeds from any sale of our securities by any selling stockholders.

7

UNAUDITED PRO FORMA CONSOLIDATED FINANCIAL INFORMATION

The following unaudited pro forma consolidated financial information applies only to offers and sales of securities prior to filing of the Company’s annual report on Form 10-K for the fiscal year ended December 25, 2022.

We have derived the unaudited consolidated pro forma statement of operations for the year ended December 26, 2021 set forth below by the application of pro forma adjustments to the audited consolidated financial statements of Portillo’s Inc. and its subsidiaries included in our Annual Report, which is incorporated by reference herein. We have derived the unaudited consolidated pro forma statement of operations for the three quarters ended September 25, 2022 set forth below by the application of pro forma adjustments to the unaudited consolidated financial statements of Portillo’s Inc. and its subsidiaries included in our quarterly report on Form 10-Q for the quarterly period ended September 25, 2022, filed with the SEC on November 3, 2022 (the “2022 Q3 Quarterly Report”), which is incorporated by reference herein.

The following unaudited pro forma consolidated statement of operations for the year ended December 26, 2021 give effect to the pro forma adjustments related to (i) the IPO and the Reorganization Transactions, which we refer to as the “IPO and Reorganization Transactions,” (ii) the offering and sale of 8,066,458 shares of Class A common stock at an offering price of $23.75 per share and the application of the net proceeds from such offering, which we refer to as the “August Secondary Offering” and (iii) the hypothetical offering and sale of 8,000,000 shares of Class A common stock (excluding shares issuable upon exercise of the underwriters’ option to purchase additional shares, if any) at an assumed offering price of $21.03 per share (which was the last sale price of our Class A common stock as reported on Nasdaq as of September 23, 2022) and the application of the net proceeds from such offering, which we refer to as the “Assumed Secondary Offering,” as if all such transactions had been completed as of December 28, 2020. We refer to the August Secondary Offering and the Assumed Secondary Offering collectively as the “Secondary Transactions.” The unaudited pro forma consolidated statement of operations for the three quarters ended September 25, 2022 presents our consolidated results of income to give pro forma effect to the Secondary Transactions, as if all such transactions had been completed as of December 27, 2021.

The unaudited pro forma balance sheet as of September 25, 2022 presents our financial position to give pro forma effect to the Assumed Secondary Offering, as if it had occurred on September 25, 2022.

The unaudited pro forma financial information has been prepared by our management and is based on Portillo’s Inc. historical financial statements and the assumptions and adjustments described in the notes to the unaudited pro forma financial information below. The presentation of the unaudited pro forma financial information is prepared in conformity with Article 11 of Regulation S-X rules effective January 1, 2021.

We based the pro forma adjustments on available information and on assumptions that we believe are reasonable under the circumstances in order to reflect, on a pro forma basis, the impact of the relevant transactions on the historical financial information of Portillo’s. See the notes to unaudited pro forma financial information below for a discussion of assumptions made. The unaudited pro forma financial information does not purport to be indicative of our results of operations or financial position had the relevant transactions occurred on the dates assumed and does not project our results of operations or financial position for any future period or date. In particular, any unaudited pro forma consolidated financial information prepared in connection with any offering occurring after the date of this prospectus may vary from the unaudited pro forma consolidated financial information presented herein as result of any differences in the characteristics of such subsequent offering from the Assumed Secondary Offering, including, but not limited to, the number of shares of our Class A common stock sold in such subsequent offering, the offering price of the shares sold in such subsequent offering and the net proceeds from any such subsequent offering.

8

The IPO and Reorganization Transactions adjustments are described in the notes to the unaudited pro forma consolidated financial information and primarily include:

The Secondary Transactions adjustments are described in the notes to the unaudited pro forma consolidated financial information and primarily include:

9

The unaudited pro forma consolidated financial information is provided for informational purposes only and is not necessarily indicative of the operating results that would have occurred if the IPO and Reorganization Transactions or the due to the Secondary Transactions adjustments had been completed as of the dates set forth above, nor is it indicative of our future results. Additionally, the unaudited pro forma consolidated financial information does not give effect to the potential impact of any anticipated synergies, operating efficiencies, or cost savings that may result.

10

UNAUDITED PRO FORMA CONSOLIDATED

STATEMENT OF OPERATIONS

See accompanying notes to unaudited pro forma financial information.

11

UNAUDITED PRO FORMA CONSOLIDATED

STATEMENT OF OPERATIONS

See accompanying notes to unaudited pro forma financial information.

12

Notes to Unaudited Pro Forma Statement of Operations

(Year Ended December 26, 2021 and Three Quarters ended September 25, 2022)

(1) Portillo’s Inc. is subject to U.S. federal income taxes, in addition to state and local taxes, with respect to its allocable share of any net taxable income of Portillo’s OpCo. The adjustment of $4.5 million to the income tax expense resulting from the IPO and Reorganization Transactions reflects our statutory tax rate of 27.9% applied to Portillo’s Inc.’s economic interest of 50.1% of Portillo’s OpCo following the IPO and Reorganization Transactions further applied to the portion of net income of Portillo’s OpCo that relates to pass-through entities whose income has not been previously subject to income tax expense for the period between December 28, 2020 and the date of the Company’s IPO.

(2) Following the consummation of the IPO and Reorganization Transactions, Portillo’s Inc. became the sole managing member of Portillo’s OpCo, and as sole managing member, the Company operates and controls all of the business and affairs of Portillo’s OpCo. As a result, Portillo’s Inc. consolidates the financial results of Portillo’s OpCo and reports a non-controlling interest representing the economic interest in Portillo’s OpCo held by the other members of Portillo’s OpCo. Following the IPO and Reorganization Transactions, we held approximately 50.1% of Portillo’s OpCo’s outstanding LLC Units, and the remaining LLC Units of Portillo’s OpCo would be held by the Continuing Pre-IPO LLC Members. Immediately following the IPO and Reorganization Transactions, the ownership percentage held by the noncontrolling interest was approximately 49.9%. Net income attributable to the noncontrolling interest represents approximately 49.9% of net income.

(3) Portillo’s Inc. is subject to U.S. federal income taxes, in addition to state and local taxes, with respect to its allocable share of any net taxable income of Portillo’s OpCo. For the year ended December 26, 2021 and the three quarters ended September 25, 2022, the pro forma adjustment of $0.5 million and $1.6 million, respectively, to the income tax expense resulting from the Secondary Transactions reflects our statutory tax rate of 27.9% applied to the additional economic interest in Portillo’s OpCo obtained in the Secondary Transactions applied to the portion of net income of Portillo’s OpCo that relates to pass-through entities whose income has not been previously subject to income tax expense.

(4) Following the Secondary Transactions, based on a weighted-average, we held approximately 66.7% of Portillo’s OpCo’s outstanding LLC Units, and the remaining LLC Units of Portillo’s OpCo are held by the Continuing Pre-IPO LLC Members. Immediately following the Secondary Transactions, based on a weighted-average, the ownership percentage held by the noncontrolling interest was approximately 33.3%. The pro forma adjustment reflects the reduction in the allocation of Portillo’s OpCo net income to the non-controlling interests. The weighted average ownership percentages for the applicable reporting periods are used to attribute net income to Portillo’s Inc. and the pre-IPO LLC Members.

(5) Pro forma basic net income per share of Class A common stock is computed by dividing the pro forma net income available to Class A common stockholders by the pro forma weighted-average shares of Class A common stock outstanding during the period. Pro forma diluted net income per share of Class A common stock is

13

computed by dividing the pro forma net income available to Class A common stockholders by the pro forma weighted-average shares of Class A common stock outstanding to give effect to potentially dilutive securities.