Filed Pursuant to Rule 424(b)(5)

Registration No. 333-289669

PROSPECTUS SUPPLEMENT

(To Prospectus dated August 22, 2025)

1,600,000 Common Shares

Pre-Funded Warrants to Purchase up to 3,254,369 Common Shares

3,254,369 Common Shares underlying the Pre-Funded Warrants

Pursuant to this prospectus supplement and the accompanying prospectus, we are offering to an accredited investor 1,600,000 of our common shares, no par value (the “Shares”) and pre-funded warrants to purchase 3,254,369 common shares (the “Pre-Funded Warrants”), including 3,254,369 of our common shares underlying the Pre-Funded Warrants.

The combined offering price of each Share, together with an accompanying Private Warrant (as defined below) is $2.06. The combined offering price of each Pre-Funded Warrant, together with an accompanying Private Warrant is $2.05999, and the exercise price per underlying share of the Pre-Funded Warrants is $0.00001 per share. Subject to limited exceptions, a holder of Pre-Funded Warrants will not have the right to exercise any portion of its Pre-Funded Warrants if the holder, together with its affiliates, would beneficially own in excess of 9.99% of the number of common shares outstanding immediately after giving effect to such exercise. This prospectus supplement also relates to the offering of common shares issuable upon the exercise of such Pre-Funded Warrants. Subject to the limitations described above, the Pre-Funded Warrants may be exercised at any time until exercised in full.

In a concurrent private placement, we are also issuing to the purchaser of the Shares and the Pre-Funded Warrants private placement warrants to purchase up to an aggregate of 4,854,369 common shares (the “Private Warrants”). The Private Warrants are immediately exercisable until the 2-year anniversary of the date of the share purchase agreement that was entered into on the date hereof, and the exercise price per underlying share of the Private Warrants is $2.06. The Private Warrants and the common shares upon the exercise of the Private Warrants (the “Private Warrant Shares”), are not being registered under the Securities Act of 1933, as amended, or the Securities Act, pursuant to the registration statement of which this prospectus supplement and the accompanying prospectus form a part, nor are such Private Warrants or Private Warrant Shares being offered pursuant to such prospectus supplement and accompanying prospectus. The Private Warrants are being offered pursuant to the exemption provided in Section 4(a)(2) of the Securities Act and/or Rule 506(b) promulgated thereunder. The Private Warrants are being sold together with the common shares and Pre-Funded Warrants being sold in this offering, and we will receive additional proceeds from the Private Warrants to the extent such Private Warrants are exercised for cash.

There is no established trading market for the Pre-Funded Warrants, and we do not expect a market to develop. We do not intend to apply for a listing for the Pre-Funded Warrants on any securities exchange or other nationally recognized trading system. Without an active trading market, the liquidity of the Pre-Funded Warrants will be limited.

We engaged Craig-Hallum Capital Group LLC to act as our exclusive placement agent (the “Placement Agent”), in connection with this offering. The Placement Agent is not purchasing the securities offered by us in this offering and is not required to arrange the purchase or sale of any specific number or dollar amount of securities, but will use its reasonable best efforts to arrange for the sale of the securities offered.

As of June 18, 2026, the aggregate market value of our outstanding common shares held by non-affiliates, or public float, was approximately $34,956,003, based on 17,395,734 common shares outstanding as of June 22, 2026, of which 1,928,476 shares were held by affiliates, and a price of $2.26 per share, which was the price at which our common shares were last sold on the Nasdaq on June 18, 2026. We have not sold any securities pursuant to General Instruction I.B.5 of Form F-3 during the prior 12-calendar-month period that ends on and includes the date of this prospectus. Accordingly, based on the foregoing, we are currently eligible under General Instruction I.B.5 of Form F-3 to offer and sell securities having an aggregate offering price of up to approximately $11,652,001. Pursuant to General Instruction I.B.5 of Form F-3, in no event will we sell securities registered on this registration statement in a public primary offering with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75 million.

Our common shares are listed on the Nasdaq Global Select Market (the “Nasdaq”) under the symbol “WPRT” and on the Toronto Stock Exchange (“TSX”) under the trading symbol “WPRT.” On June 22, 2026, the last reported sale price of our common shares on the Nasdaq was $2.04 per share and on the TSX was C$2.88 per share.

We are a “foreign private issuer” as defined under the U.S. federal securities laws and, as such, may elect to comply with certain reduced public company disclosure and reporting requirements.

Investing in our securities involves risks. Please read “Risk Factors” beginning on page S-4 of this prospectus supplement and in the documents incorporated by reference into this prospectus supplement.

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

Delivery of the securities is expected to be made on or about June 23, 2026.

The date of this prospectus supplement is June 22, 2026.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

PROSPECTUS 

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is the prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documents incorporated by reference, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. Before you invest, you should carefully read this prospectus supplement, the accompanying prospectus, all information incorporated by reference herein and therein, as well as the additional information described under “Where You Can Find More Information; Incorporation by Reference” on page S-21 of this prospectus supplement. These documents contain information you should consider when making your investment decision. This prospectus supplement may add, update or change information contained in the accompanying prospectus or any documents incorporated by reference. To the extent that any statement that we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying prospectus and such documents incorporated by reference.

You should rely only on the information contained or incorporated by reference in this prospectus supplement, the accompanying prospectus and in any free writing prospectuses we may provide to you in connection with this offering. Neither we nor the Placement Agent have authorized any other person to provide you with any information that is different. If anyone provides you with different or inconsistent information, you should not rely on it. We are offering to sell, and seeking offers to buy, the securities offered hereby only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the offering of the securities offered hereby in certain jurisdictions may be restricted by law. 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 securities offered hereby and the distribution of this prospectus supplement outside the United States. This prospectus supplement does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

Unless otherwise indicated, information contained in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference concerning our industry and the markets in which we operate, including our general expectations and market position, market opportunity and market share, is based on information from our own management estimates and research, as well as from industry and general publications and research, surveys and studies conducted by third parties. Management estimates are derived from publicly available information, our knowledge of our industry and assumptions based on such information and knowledge, which we believe to be reasonable. In addition, assumptions and estimates of our and our industry’s future performance are necessarily subject to a high degree of uncertainty and risk due to a variety of factors, including those described in “Risk Factors” in this prospectus supplement, the accompanying prospectus and in our Annual Report on Form 20-F for the year ended December 31, 2025 and our subsequent filings under the Exchange Act which are incorporated by reference into this prospectus supplement. These and other important factors could cause our future performance to differ materially from our assumptions and estimates. See “Special Note Regarding Forward-Looking Statements.”

In this prospectus supplement, unless the context otherwise indicates, the terms “Westport Fuel Systems,” the “Company,” “we,” “our” and “us” or similar terms refer to Westport Fuel Systems Inc.

Unless otherwise indicated, all references to “$” and “dollars” in this prospectus supplement mean United States dollars. References to “C$” in this prospectus supplement means Canadian dollars.

We are a “foreign private issuer” under SEC rules. As such, we are exempt from the rules and regulations under the Exchange Act prescribing the furnishing and content of proxy statements, and our officers, directors and principal shareholders are exempt from the reporting and “short-swing” profit recovery provisions contained in Section 16 of the Exchange Act with respect to their purchase and sale of our common shares. In addition, we are not required to file reports and financial statements with the SEC as frequently or as promptly as U.S. public companies whose securities are registered under the Exchange Act.

The securities offered by this prospectus supplement and the accompanying prospectus have not been and will not be qualified for sale under the securities laws of any province or territory of Canada or to any resident of Canada and may not be offered or sold, directly or indirectly, in Canada, or to or for the account of any resident of Canada. This prospectus supplement and the accompanying prospectus have not been filed in respect of, and will not qualify, any distribution of these securities in any province or territory of Canada.

RISK FACTORS

Investing in our securities involves a high degree of risk. Before investing in our securities, you should consider carefully the risks described below, together with the other information contained in this prospectus supplement, the accompanying prospectus or incorporated by reference herein or therein, including the risks and uncertainties discussed under “Risk Factors” contained in our Annual Report on Form 20-F for the year ended December 31, 2025 as updated by our subsequent filings under the Exchange Act, which are incorporated by reference into this prospectus supplement. If any of the risks incorporated by reference or set forth below occur, our business, financial condition, results of operations and future growth prospects could be materially and adversely affected. In these circumstances, the market price of our securities could decline, and you may lose all or part of your investment.

Risks Related to this Offering and our Securities

You will experience immediate and substantial dilution as a result of this offering and may experience additional dilution in the future.

Because the price per share of our common shares being offered is higher than the book value per share of our common shares, you will suffer substantial dilution in the net tangible book value of the common shares you purchase in this offering. After giving effect to the sale by us of 1,600,000 common shares at the public offering price of $2.06 per share and Pre-Funded Warrants to purchase 3,254,369 shares of our common shares for $2.06 per share (which equals the $2.05999 per underlying share purchase price, plus the $0.00001 per underlying share exercise price) (including the common shares issuable upon exercise of the Pre-Funded Warrants and resulting proceeds, but excluding any resulting accounting associated with the Pre-Funded Warrants and without giving effect to any exercise of the Private Warrants described elsewhere in this prospectus supplement), less the Placement Agent fees and estimated offering expenses payable by us in each case, if you purchase securities in this offering, you will suffer immediate and substantial dilution of $1.17 per share, representing the difference between the public offering price per share of $2.06 and the as adjusted net tangible book value per share of our common shares of $3.23 as of March 31, 2026. See “Dilution” below for a more detailed discussion of the dilution you will incur if you purchase our common shares and Pre-Funded Warrants in the offering.

In addition, we are selling private placement warrants to purchase 4,854,369 common shares (the “Private Warrants”), in a concurrent private placement to the same investor as is purchasing the Shares and the Pre-Funded Warrants, and we may in the future offer additional common shares or other securities convertible into or exchangeable for our common shares at prices that may not be the same as the price per share in this offering. In the event that the Private Warrants or the other outstanding options or warrants are exercised or settled, or that we make additional issuances of common shares or other convertible or exchangeable securities, you could experience additional dilution. We cannot assure you that we will be able to sell shares or other securities in any other offering at a price per share that is equal to or greater than the price per share paid in this offering, and investors purchasing shares or other securities in the future could have rights superior to existing shareholders, including the investor who purchases Shares and Pre-Funded Warrants in this offering. The price per share at which we sell additional common shares or securities convertible into common shares in future transactions, may be higher or lower than the price per share in this offering. As a result, purchasers of the Shares and Pre-Funded Warrants we sell, as well as our existing shareholders, will experience significant dilution if we sell at prices significantly below the price at which they invested. See “Dilution” below for a more detailed illustration of the dilution you would incur if you participate in this offering.

There is no public market for the Pre-Funded Warrants being sold in this offering or the Private Warrant being sold in a private placement concurrently with this offering.

There is no established public trading market for the Pre-Funded Warrants being offered in this offering or the Private Warrants being offered in the concurrent private placement, and we do not expect a market to develop. In addition, we do not intend to apply for listing of the Pre-Funded Warrants or Private Warrants on any national securities exchange or other nationally recognized trading system. Without an active market, the liquidity of the Pre-Funded Warrants and Private Warrants will be limited.

We will not receive any meaningful amount of additional funds upon the exercise of the Pre-Funded Warrants.

Each Pre-Funded Warrant will be exercisable until it is fully exercised and by means of payment of the nominal cash purchase price upon exercise or by means of a “cashless exercise” according to a formula set forth in the Pre-Funded Warrant. Accordingly, we will not receive any meaningful additional funds upon the exercise of the Pre-Funded Warrants.

We have broad discretion to determine how to use the funds raised in this offering and the concurrent private placement, and may use them in ways that may not enhance our operating results or the price of our common shares.

Our management will have broad discretion over the use of proceeds from this offering and the concurrent private placement, and we could spend the proceeds from this offering and the concurrent private placement in ways our shareholders may not agree with or that do not yield a favorable return, if at all. We intend to use the net proceeds as described under the heading “Use of Proceeds.” However, our use of these proceeds may differ substantially from our current plans. If we do not invest or apply the proceeds of this offering and the concurrent private placement in ways that improve our operating results, we may fail to achieve expected financial results, which could cause our stock price to decline and could have an adverse effect on the market price of our common shares.

Any holder of the Pre-Funded Warrants and Private Warrants will have no rights as a holder of our common shares until such holder exercises its Pre-Funded Warrants and/or Private Warrants and acquires our common shares.

Until the holder of any Pre-Funded Warrants or Private Warrants exercises such Pre-Funded Warrants and/or Private Warrants and acquires our common shares, such holder will have no rights with respect to the common shares underlying such Pre-Funded Warrants or Private Warrants. Upon exercise of such Pre-Funded Warrants or Private Warrants, the holder will be entitled to exercise the rights of a holder of our common shares only as to matters for which the record date occurs after the exercise date.

A significant holder or beneficial holder of our common shares may not be permitted to exercise the Pre-Funded Warrants or Private Warrants that it holds.

A holder of the Pre-Funded Warrants and/or Private Warrants will not be entitled to exercise any portion of the Pre-Funded Warrants or Private Warrants that, upon giving effect to such exercise, would cause the aggregate number of shares of our common shares beneficially owned by such holder (together with its affiliates and any other persons whose beneficial ownership of common shares would be aggregated with the holder for purposes of Section 13(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act) to exceed 9.99% (in the case of the Pre-Funded Warrants or Private Warrants) of the total number of then issued and outstanding common shares, as such percentage ownership is determined in accordance with the terms of the Pre-Funded Warrants or Private Warrants and subject to such holder’s rights under the Pre-Funded Warrants and Private Warrants to increase or decrease such percentage to any other percentage not in excess of 9.99% upon at least 61 days’ prior notice from such holder to us. As a result, a holder may not be able to exercise its Pre-Funded Warrants or Private Warrants for our common shares at a time when it would be financially beneficial for such holder to do so. In such a circumstance, a holder could seek to sell its Pre-Funded Warrants or Private Warrants to realize value, but it may be unable to do so in the absence of an established trading market.

This offering may cause the trading price of our common shares to decrease.

The price per share, together with the number of Shares and Pre-Funded Warrants we propose to issue and ultimately will issue if this offering is completed and/or the number of our common shares issuable upon exercise of the Private Warrants being sold concurrently herewith, may result in an immediate decrease in the market price of our common shares. This decrease may continue after the completion of this offering.

If we do not file and maintain a current and effective prospectus relating to the common shares issuable upon exercise of the Private Warrants, the holder thereof may exercise the Private Warrants on a “cashless basis.”

If we do not file and maintain a current and effective prospectus relating to the common shares issuable upon exercise of the Private Warrants at the time that holders wish to exercise such warrants, they will be able to exercise such warrants on a “cashless basis”. As a result, the number of common shares that holders will receive upon exercise of the Private Warrants will be fewer than it would have been had such holders exercised their Private Warrants for cash. We have agreed to file a registration statement to register the common shares underlying the Private Warrants (the “Private Warrant Shares”) as soon as practicable (and in any event within 30 calendar days of the closing date of this offering), and use commercially reasonable efforts to cause such registration statement to become effective by the earlier of (a) the 60th calendar day following the initial filing date if the SEC notifies the Company that it will review such registration statement and (b) the fifth business day after the Company is notified by the SEC that such registration statement will not be reviewed and to keep such registration statement effective at all times until the investor holds no Private Warrants or Private Warrant Shares issuable upon exercise thereof. However, we cannot assure you that we will be able to do so. If the Private Warrants are exercised on a “cashless” basis, we will not receive any consideration from such exercises.

Provisions of the Private Warrant could discourage an acquisition of us by a third party.

Certain provisions of the Private Warrants being sold in a private offering concurrently with this offering could make it more difficult or expensive for a third party to acquire us. The Private Warrants prohibit us from engaging in certain transactions constituting “fundamental transactions” unless, among other things, the surviving entity assumes our obligations under the Private Warrants. Further, the Private Warrants provide that, in the event of “fundamental transaction,” with some exceptions, we or a successor entity will be obligated to, at the option of the holder of such warrant, purchase such warrant from such holder by paying an amount of cash equal to the Black Scholes value (as described in such warrants) of the unexercised portion of the Private Warrant on the date of the consummation of the fundamental transaction. For more information, see “Private Placement Transaction”. These and other provisions of the Private Warrants could prevent or deter a third party from acquiring us even where the acquisition could be beneficial to the holders of our common shares.

There may be future sales of our common shares, which could adversely affect the market price of our common shares and dilute a shareholder’s ownership of common shares.

The exercise of any warrants or options granted to executive officers and other service providers under our equity compensation plans, and any other issuances of our common shares could have an adverse effect on the market price of the shares of our common shares. Other than the restrictions set forth in the section titled “Plan of Distribution,” we are not restricted from issuing additional common shares, including any securities that are convertible into or exchangeable for, or that represent the right to receive common shares, provided that we are subject to the requirements of the Nasdaq Global Select Market (which generally requires shareholder approval for any transactions which would result in the issuance of more than 20% of our then outstanding common shares or voting rights representing over 20% of our then outstanding common shares). Sales of a substantial number of our common shares in the public market or the perception that such sales might occur could materially adversely affect the market price of our common shares. Because our decision to issue securities in any future offering will depend on market conditions and other factors beyond our control, we cannot predict or estimate the amount, timing or nature of our future offerings. Accordingly, our shareholders bear the risk that our future offerings will reduce the market price of our common shares and dilute their stock holdings in us.

The market price of the common shares may be subject to significant fluctuations in response to variations in our financial results or other factors.

The market price of the common shares may be volatile, which may affect the ability of holders of common shares to sell their common shares at an advantageous price. Market price fluctuations in the common shares may be due to our operating results failing to meet the expectations of securities analysts or investors in any quarter, downward revision in securities analysts' estimates, governmental regulatory action, adverse changes in general market conditions or economic trends, including changes resulting from global geopolitical events, acquisitions, dispositions or other material public announcements by us or our competitors, along with a variety of additional factors, including, without limitation, those set forth under “Special Note Regarding Forward-Looking Statements” in this prospectus supplement.

In recent years, the securities markets in the United States and Canada have experienced a high level of price and volume volatility, and the market prices of securities of many technology companies have experienced wide fluctuations in price which have not necessarily been related to the operating performance, underlying asset values or prospects of such companies. There can be no assurance that continuing fluctuations in price will not occur. These factors are ultimately beyond our control and could have a material adverse effect on our financial condition and results of operations.

Management identifies a material uncertainty regarding our ability to continue as a going concern.

Management continues to identify a material uncertainty that raises substantial doubt about the Company's ability to continue as a going concern. Based on our projected capital expenditures, debt servicing obligations and operating requirements under our current business plan, we anticipate that our cash and cash equivalents will not be sufficient to fund our operations through the next twelve months from the date of our unaudited condensed consolidated financial statements for the three-month period ended March 31, 2026. We may need to raise additional funding in order to continue as a going concern and we cannot provide any assurance that we will be successful in doing so. If we are unable to improve our liquidity position when required, we may not be able to continue as a going concern.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

Certain statements contained in this prospectus supplement, the prospectus and the documents incorporated by reference herein and therein constitute “forward-looking statements” within the meaning of the United States Private Securities Litigation Reform Act of 1995, as amended (collectively referred to as, “forward-looking statements”). When used in such documents, the words “may”, “would”, “could”, “will”, “intend”, “plan”, “anticipate”, “believe”, “estimate”, “expect”, “project” and similar expressions, as they relate to us or our management, are intended to identify forward-looking statements. In particular, this prospectus supplement and the prospectus and the documents incorporated by reference contain forward-looking statements which include, but are not limited to, the expected benefits of hydrogen use in internal combustion engines, the progress, timing and outcomes of on-road testing, integration, and development activities, the timing and likelihood of potential future commercialization and launch of hydrogen-powered heavy-duty trucks, the ability for hydrogen HPDI fuel system technology to support decarbonization objectives and to be classified as a zero-emissions vehicle under applicable standards, the anticipated effect of the offering on our performance, our future market opportunities, our ability to continue our business as a going concern and generate sufficient cash flows to fund operations; and the availability of funding and funding requirements.

Such statements reflect our current views with respect to future events and are subject to certain risks, uncertainties and assumptions. Actual results may differ materially from those expressed in these forward-looking statements due to several uncertainties and risks, including the risks described in this prospectus supplement, the prospectus and the documents incorporated by reference herein and therein and other unforeseen risks. Such risks, uncertainties, factors and assumptions include, without limitation:

Readers are cautioned that forward-looking statements are not based on historical facts but instead are based on reasonable assumptions, estimates, analysis and opinions of our management at the time they were provided or made, in light of its experience and its perception of trends, current conditions and expected developments, as well as other factors that management believes to be relevant and reasonable in the circumstances, and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements, as applicable, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements.

Readers are cautioned that the foregoing lists are not exhaustive of all factors and assumptions that may have been used. Although we have attempted to identify important factors that could cause actual results to differ materially, there may be other factors that cause results not to be as anticipated, estimated or intended. There can be no assurance that such forward-looking statements will prove to be accurate as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements. The forward-looking statements contained in this prospectus supplement, the prospectus and the documents incorporated by reference herein and therein are presented for the purposes of assisting readers in understanding our expected financial and operating performance and our plans and objectives and may not be appropriate for other purposes.

Any forward-looking statement is made only as of the date of this prospectus supplement, the prospectus or the applicable document incorporated by reference herein or therein, unless otherwise indicated in such documents, and represent the views and expectations of our management. We undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as otherwise required by applicable law.

USE OF PROCEEDS

We estimate that the net proceeds to us from this offering, after deducting Placement Agent fees and paying estimated offering expenses payable by us, will be approximately $8.9 million, assuming the exercise in full of the Pre-Funded Warrants and not including any funds we may receive as a result of the exercise of the Private Warrants.

We intend to use the net proceeds of this offering for working capital and other general corporate purposes.

The amounts and timing of our actual expenditures will depend on numerous factors, including the factors described under “Risk Factors” in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, as well as the amount of cash used in our operations. We may find it necessary or advisable to use the net proceeds for other purposes, and we will have broad discretion in the application of the net proceeds. Pending the uses described above, we plan to invest the net proceeds from this offering in short- and intermediate-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or government securities. In addition, while we have not entered into any agreements, commitments or understandings relating to any significant transaction as of the date of this prospectus supplement, we may use a portion of the net proceeds to pursue acquisitions, joint ventures and other strategic transactions.

DIVIDEND POLICY

We intend to retain future earnings, if any, to finance the operation and expansion of our business and do not anticipate paying any cash dividends in the foreseeable future. Any future determination related to our dividend policy will be made at the discretion of our board of directors after considering our financial condition, results of operations, capital requirements, business prospects and other factors the board of directors deems relevant, and subject to the restrictions contained in any future financing instruments.

DILUTION

If you invest in this offering, your ownership interest will be immediately diluted to the extent of the difference between the public offering price per Share and/or per underlying share of the Pre-Funded Warrants and the as adjusted net tangible book value per share after giving effect to this offering.

As of March 31, 2026, we had a net tangible book value of $62.9 million, or $3.61 per common share. Our net tangible book value per share represents total tangible assets less total liabilities, divided by the number of common shares outstanding at March 31, 2026, after giving effect to the assumptions set forth below.

After giving effect to the issuance and sale by us of 1,600,000 common shares at a public offering price of $2.06 per share in this offering, and Pre-Funded Warrants to purchase 3,254,369 common shares for $2.06 per share (which equals the $2.05999 purchase price, plus the $0.00001 exercise price) (including the common shares issuable upon exercise of the Pre-Funded Warrants and resulting proceeds, but excluding any resulting accounting associated with the Pre-Funded Warrants and without giving effect to any exercise of the Private Warrants described elsewhere in this prospectus supplement), less the Placement Agent fees and estimated offering expenses payable by us, our as adjusted net tangible book value as of March 31, 2026 would have been approximately $71.8 million, or approximately $3.23 per share. This amount represents an immediate decrease in net tangible book value of $0.38 per share to our existing stockholders and an immediate dilution in net tangible book value of approximately $1.17 per share to new investors purchasing common shares in this offering.

All calculations of dilution in this prospectus supplement assume the sale of all of the shares and Pre-Funded Warrants offered in this offering. The following table illustrates this dilution on a per share basis:

The number of common shares to be outstanding after this offering is based on 17,395,734 of our common shares outstanding as of March 31, 2026, and excludes:

Except as otherwise indicated, all information in this prospectus supplement assumes no exercise of the Private Warrants, no exercise of outstanding options or warrants to purchase common shares, settlement of share units, or issuance of shares reserved for future awards.

To the extent that outstanding options or warrants are exercised, share units are settled, or we issue shares pursuant to our equity incentive plan, you may experience further dilution. In addition, we may choose to raise additional capital because of market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans. If we raise additional capital through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our securityholders. To the extent that we issue additional common shares under our equity incentive plans, through the establishment of an at-the-market program, or upon the exercise of options, there will be further dilution to investors in this offering.

DESCRIPTION OF THE SECURITIES WE ARE OFFERING

We are offering through this prospectus supplement and the accompanying prospectus (i) 1,600,000 common shares, and (ii) Pre-Funded Warrants to purchase up to 3,254,369 of our common shares, including the 3,254,369 common shares underlying the Pre-Funded Warrants. We are also registering the common shares issuable from time to time upon exercise of the Pre-Funded Warrants offered hereby.

Common Shares

The material terms and provisions of our common shares and each other class of our securities that qualifies or limits our common shares are described under the caption “Description of Common Shares” starting on page 10 of the accompanying prospectus.

Pre-Funded Warrants

The following summary of certain terms and provisions of Pre-Funded Warrants that are being offered hereby is not complete and is subject to, and qualified in its entirety by, the provisions of the Pre-Funded Warrants, the form of which will be filed with the SEC as an exhibit to a Report on Form 6-K in connection with this offering and incorporated by reference into the registration statement of which this prospectus supplement and the accompanying prospectus form a part. Prospective investors should carefully review the terms and provisions of the form of Pre-Funded Warrants for a complete description of the terms and conditions of the Pre-Funded Warrants.

Duration and Exercise Price

The Pre-Funded Warrant offered hereby will have an initial exercise price of $0.00001 per share. The Pre-Funded Warrants will be immediately exercisable and may be exercised at any time until the Pre-Funded Warrants are exercised in full. The exercise price and number of common shares issuable upon exercise is subject to appropriate adjustment in the event of stock dividends, stock splits, reorganizations or similar events affecting our common shares and the exercise price.

Exercisability

The Pre-Funded Warrant will be exercisable, at the option of each holder, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full for the number of common shares purchased upon such exercise (except in the case of a cashless exercise as discussed below).

A holder (together with its affiliates) may not exercise any portion of the Pre-Funded Warrants to the extent that the holder would beneficially own more than 9.99% of the outstanding common shares immediately after exercise (the “Beneficial Ownership Limitation”), except that upon at least 61 days’ prior notice from the holder to us, the holder may increase the Beneficial Ownership Limitation, provided that the Beneficial Ownership Limitation in no event exceeds 9.99%.

Cashless Exercise

In lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may, in its sole discretion, instead elect, to receive upon such exercise (either in whole or in part) the net number of common shares determined according to a formula set forth in the Pre-Funded Warrants. No fractional common shares will be issued in connection with the exercise of the Pre-Funded Warrants. In lieu of fractional shares, we will pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share. 

Fundamental Transaction

In the event of a fundamental transaction, as described in the Pre-Funded Warrants and generally including any reorganization, recapitalization or reclassification of our common shares, the sale, transfer or other disposition of all or substantially all of our properties or assets, our consolidation or merger with or into another person, the acquisition of more than 50% of our outstanding voting securities, the holders of the Pre-Funded Warrants will be entitled to receive upon exercise of the Pre-Funded Warrants the kind and amount of securities, cash or other property that the holders would have received had they exercised the Pre-Funded Warrants immediately prior to such fundamental transaction. 

Transferability

Subject to applicable laws, each Pre-Funded Warrant may be transferred at the option of the holder upon surrender of such Pre-Funded Warrant to us together with the appropriate instruments of transfer.

Exchange Listing

We do not intend to list the Pre-Funded Warrants on any securities exchange or nationally recognized trading system.

Rights as a Shareholder

Except as otherwise provided in the Pre-Funded Warrants or by virtue of such holder’s ownership of common shares, the holders of the Pre-Funded Warrants do not have the rights or privileges of holders of our common shares, including any voting rights, until they exercise the Pre-Funded Warrants.

PRIVATE PLACEMENT TRANSACTION

Concurrently with the sale of common shares and Pre-Funded Warrants in this offering, we will issue to the investor in this offering private placement warrants, or Private Warrants, to purchase up to an aggregate of 4,854,369 common shares at an exercise price equal to $2.06 per share (subject to standard adjustments for stock splits, stock dividend, rights offerings and pro rata distributions). The Private Warrants are being sold together with the Shares and Pre-Funded Warrants being sold in this offering, and we will receive additional proceeds from the Private Warrants to the extent such Private Warrants are exercised for cash.

The Private Warrants and the common shares issuable upon the exercise of such Private Warrants are not being registered under the Securities Act, are not being offered pursuant to this prospectus supplement and the accompanying prospectus and instead are being offered pursuant to the exemption provided in Section 4(a)(2) under the Securities Act and/or Rule 506(b) promulgated thereunder. Accordingly, the purchasers may only sell common shares issued upon exercise of the Private Warrants pursuant to an effective registration statement under the Securities Act covering the resale of those shares, an exemption under Rule 144 under the Securities Act or another applicable exemption under the Securities Act.

The summary below is not complete and is subject to, and qualified in its entirety by, the provisions of the Private Warrants, which will be filed with the SEC as an exhibit to a Report on Form 6-K in connection with the concurrent private placement and incorporated by reference into the registration statement of which this prospectus supplement and the accompanying prospectus form a part. Prospective investors should carefully review the terms and provisions of the form of Private Warrants for a complete description of the terms and conditions of the Private Warrants.

Duration, Exercise Price and Anti-Dilutive Rights

The Private Warrants have an exercise price of $2.06 per share and will be immediately exercisable. The Private Warrants will expire on June 23, 2028, the second anniversary of the date on which the Private Warrants will be issued and become exercisable. The Private Warrants contain standard adjustments to the exercise price including for stock splits, stock dividend, rights offerings and pro rata distributions.

Exercisability

The Private Warrants will be immediately exercisable, at the option of each holder and until the expiration date, in whole or in part, by delivering to us a duly executed exercise notice accompanied by payment in full for the number of common shares purchased upon such exercise (except in the case of a cashless exercise as discussed below).

Exercise Limitation

A holder (together with its affiliates) may not exercise any portion of the Private Warrants to the extent that the holder would beneficially own more than 9.99% of the outstanding common shares immediately after exercise (the “Beneficial Ownership Limitation”), except that upon at least 61 days’ prior notice from the holder to us, the holder may increase the Beneficial Ownership Limitation, provided that the Beneficial Ownership Limitation in no event exceeds 9.99%.

Cashless Exercise

In lieu of making the cash payment otherwise contemplated to be made to us upon such exercise in payment of the aggregate exercise price, the holder may, in the event the shares underlying the Private Warrants, or the Private Warrant Shares, are not registered under the Securities Act, elect instead to receive upon such exercise (either in whole or in part) the net number of common shares determined according to a formula set forth in the Private Warrants. No fractional common shares will be issued in connection with the exercise of a Private Warrant. In lieu of fractional shares, we will pay the holder an amount in cash equal to the fractional amount multiplied by the exercise price or round up to the next whole share.

Fundamental Transaction

In the event of a fundamental transaction, as described in the Private Warrants and generally including any reorganization, recapitalization or reclassification of our common shares, the sale, transfer or other disposition of all or substantially all of our properties or assets, our consolidation or merger with or into another person, the acquisition of more than 50% of our outstanding voting securities, the holders of the Private Warrant will be entitled to receive upon exercise of the Private Warrant the kind and amount of securities, cash or other property that the holders would have received had they exercised the Private Warrant immediately prior to such fundamental transaction. In addition, in the event of a fundamental transaction, with some exceptions, we or a successor entity will be obligated to, at the option of the holder of such warrant, purchase such warrant from such holder by paying an amount of cash equal to the Black Scholes value (as described in such warrants) of the unexercised portion of the Private Warrant on the date of the consummation of the fundamental transaction.

Transferability

Subject to applicable laws, a Private Warrant may be transferred at the option of the holder upon surrender of the Private Warrant to us together with the appropriate instruments of transfer.

Resale/Registration Rights

Under the purchase agreement pursuant to which the Private Warrant was sold, or the Purchase Agreement, we agreed that as soon as practicable (and in any event within 30 calendar days of the closing date of this offering), we would file a registration statement on Form F-1 or Form F-3 (the “Re-Sale Registration Statement”), providing for the resale of the common shares issuable upon exercise of the Private Warrants, use commercially reasonable efforts to cause such registration statement to become effective by the earlier of (a) the 60th calendar day following the initial filing date if the SEC notifies the Company that it will review such registration statement and (b) the fifth business day after the Company is notified by the SEC that such registration statement will not be reviewed and to keep such registration statement effective at all times until the investor holds no Private Warrants or Private Warrant Shares issuable upon exercise thereof.

Exchange Listing

We do not intend to list the Private Warrants on any securities exchange or nationally recognized trading system.

Rights as a Shareholder

Except as otherwise provided in the Private Warrants or by virtue of such holder’s ownership of common shares, the holders of the Private Warrants do not have the rights or privileges of holders of our common shares, including any voting rights, until they exercise the Private Warrants.

PLAN OF DISTRIBUTION

We have engaged Craig-Hallum Capital Group LLC (the “Placement Agent”) to act as our exclusive placement agent in connection with this offering. The Placement Agent is not purchasing the securities offered by us in this offering, and is not required to sell any specific number or dollar amount of securities, but will assist us in this offering on a best-efforts basis. The terms of this offering were subject to market conditions and negotiations between us, the Placement Agent and prospective investors. The Placement Agent may engage sub-agents or selected dealers to assist with this offering. We may not sell the entire amount of the securities offered pursuant to this prospectus supplement.

The Placement Agent proposes to arrange for the sale of the shares we are offering pursuant to this prospectus supplement and accompanying prospectus to one or more institutional or accredited investors through securities purchase agreements directly between the purchaser and us. We will only sell to such investors who have entered into the securities purchase agreement with us.

We have agreed to indemnify the Placement Agent against specified liabilities and to contribute to payments the Placement Agent may be required to make in respect thereof.

Pursuant to the terms of the securities purchase agreement, from the date of the securities purchase agreement until 60 days after the closing date of this offering, we may not issue, enter into any agreement to issue or announce the issuance or proposed issuance of any common shares or common shares equivalents or file any registration statement or any amendment or supplement thereto, subject to certain exceptions set forth in the securities purchase agreement.

In addition, we have also agreed with the purchasers of our common shares, subject to certain exceptions, from the date of the securities purchase agreement until 60 days after the closing date of this offering, that we will not effect or enter into an agreement to effect a “Variable Rate Transaction” as defined in the securities purchase agreement.

Each of our directors and executive officers have agreed to be subject to a lock-up period of 60 days following the date of the closing date of this offering, subject to certain exceptions

Fees and Expenses

We have agreed to pay the Placement Agent a placement agent fee equal to 6.0% of the aggregate purchase price of the securities sold in this offering. The following table shows the per share and total cash Placement Agent’s fees we will pay to the Placement Agent in connection with the sale of the securities offered pursuant to this prospectus supplement and the accompanying prospectus, assuming the purchase of all of the securities offered hereby.

(1) We have also agreed to reimburse the Placement Agent for certain expenses incurred in connection with this offering, discussed below. In addition, in connection with any future exercise of the Private Warrants, we have agreed to pay the Placement Agent a cash fee equal to 3.0% of the aggregate gross exercise price paid in cash with respect to the exercise of such Private Warrants.

We have also agreed to reimburse the Placement Agent up to $100,000 for its accountable expenses incurred in connection with the performance of its services under the engagement letter, excluding expenses related to blue sky compliance and FINRA filings. We estimate that the total expenses of the offering payable by us, excluding the Placement Agent’s fees and expenses, will be approximately $0.5 million.

Regulation M Restrictions

The placement agent may be deemed to be an underwriter within the meaning of Section 2(a)(11) of the Securities Act, and any commissions received by it and any profit realized on the sale of our securities offered hereby by it while acting as principal might be deemed to be underwriting discounts or commissions under the Securities Act. The placement agent will be required to comply with the requirements of the Securities Act and the Exchange Act, including, without limitation, Rule 10b-5 and Regulation M under the Exchange Act. These rules and regulations may limit the timing of purchases and sales of our securities by the placement agent. Under these rules and regulations, the placement agent may not (i) engage in any stabilization activity in connection with our securities; or (ii) bid for or purchase any of our securities or attempt to induce any person to purchase any of our securities, other than as permitted under the Exchange Act, until they have completed their participation in the distribution.

Electronic Distribution

This prospectus supplement and accompanying prospectuses may be made available in electronic format on websites or via email or through other online services maintained by us and/or the placement agent. Other than this prospectus supplement and the accompanying prospectuses in electronic format, the information on our and/or the placement agent’s websites and any information contained in any other websites maintained by our and/or the placement agent is not part of this prospectus supplement, accompanying prospectuses, or the registration statements of which this prospectus supplement and accompanying prospectuses form a part, has not been approved or endorsed by us or the placement agent, and should not be relied upon by investors.

The foregoing does not purport to be a complete statement of the terms and conditions of the placement agency agreement with the placement agent nor the securities purchase agreement. See “Where You Can Find More Information.”

Price Stabilization, Short Positions

No person has been authorized by us to engage in any form of price stabilization in connection with this offering.

Relationships

The Placement Agent and its affiliates may provide from time to time in the future certain commercial banking, financial advisory, investment banking and other services for us in the ordinary course of their business, for which they may receive customary fees and commissions. In addition, from time to time, the Placement Agent and its affiliates may effect transactions for their own accounts or the account of customers, and hold on behalf of themselves or their customers, long or short positions in our debt or equity securities or loans, and may do so in the future. Except as disclosed in this prospectus supplement, we have no present arrangements with the Placement Agent for any further services.

Transfer Agent and Registrar

Our transfer agent and registrar for our Common Shares is Computershare Trust Company of Canada at its principal offices in Vancouver, British Columbia, Calgary, Alberta and Toronto, Ontario. Our U.S. transfer agent is Computershare Trust Company, N.A. 350 Indiana Street, Suite 750, Golden, CO 80401

Listing

Our common shares are listed on the Nasdaq under the symbol “WPRT” and on the TSX under the trading symbol “WPRT.”

CAPITALIZATION

The following table sets forth our consolidated capitalization as of March 31, 2026 on an actual basis and on an as adjusted basis to give effect to the issuance and sale by us of 1,600,000 common shares at a public offering price of $2.06 per share in this offering, and Pre-Funded Warrants to purchase 3,254,369 common shares for $2.06 per share (which equals the $2.05999 per underlying share purchase price, plus the $0.00001 per underlying share exercise price), after deducting Placement Agent fees and estimated offering expenses payable by us. The following table is based on our unaudited condensed consolidated interim balance sheet as at March 31, 2026 and should be read in conjunction with other information included in the documents incorporated by reference in this prospectus supplement.

SUPPLEMENTAL FEDERAL INCOME TAX CONSIDERATIONS

The following is a general summary of certain U.S. federal income tax considerations regarding the purchase, ownership or disposition of the Pre-Funded Warrants. This discussion is a supplement to, and is intended to be read together with, the discussion appearing under the caption “Taxation—U.S. Federal Income Tax Considerations” in our Annual Report on Form 20-F for the year ended December 31, 2025 as updated by our subsequent filings under the Exchange Act, which are incorporated by reference into this prospectus supplement. Prospective investors should carefully review this discussion and the discussion under the caption “Taxation—U.S. Federal Income Tax Considerations” in our Annual Report on Form 20-F for the year ended December 31, 2025 before acquiring any Pre-Funded Warrants pursuant to this prospectus supplement and the accompanying prospectus.

Each capitalized term used but not defined in this “Supplemental Federal Income Tax Considerations” section has the meaning ascribed thereto in our Annual Report on Form 20-F for the year ended December 31, 2025.

Pre-Funded Warrants

Although it is not entirely free from doubt, the Pre-Funded Warrants should be treated as our Common Shares for U.S. federal income tax purposes, and a holder of the Pre-Funded Warrants should generally be taxed in the same manner as a holder of such Common Shares, as described below. Accordingly, no gain or loss should be recognized (other than with respect to any cash paid in lieu of a fractional share) upon the exercise of the Pre-Funded Warrants and, upon exercise, the holding period of the Pre-Funded Warrants should carry over to the Common Shares received. Similarly, the tax basis of the Pre-Funded Warrants should carry over to the Common Shares received upon exercise, increased by the exercise price per share of our Common Shares.

Our characterization is not binding on the IRS, and the IRS may treat the Pre-Funded Warrants as warrants to acquire our Common Shares. In that case, the amount and character of your gain or loss with respect to an investment in the Pre-Funded Warrants could be materially different from the discussion set forth below. Accordingly, each holder should consult such holder’s tax advisor regarding the risks associated with the acquisition of the Pre-Funded Warrants pursuant to this offering (including potential alternative characterizations). The remainder of this discussion assumes that the Pre-Funded Warrants are treated as our Common Shares for U.S. federal income tax purposes. Accordingly, references to “Common Shares” under the caption “Taxation—U.S. Federal Income Tax Considerations” in our Annual Report on Form 20-F for the year ended December 31, 2025 generally include the Pre-Funded Warrants.

Constructive Distributions on Pre-Funded Warrants.

A U.S. Holder of Pre-Funded Warrants may, in some circumstances, be deemed to have received a distribution subject to U.S. federal income tax as a result of an adjustment or the non-occurrence of an adjustment to the exercise price or number of shares of Common Shares issuable upon exercise of such Pre-Funded Warrants. U.S. Holders should consult their tax advisors regarding the proper treatment of any adjustments or the non-occurrence of an adjustment to Pre-Funded Warrants.

Prospective investors in the Pre-Funded Warrants should consult their tax advisors regarding the U.S. federal income and other tax consequences to them of the acquisition, ownership and disposition of the Pre-Funded Warrants offered by this prospectus supplement and the accompanying prospectus.

LEGAL MATTERS

The validity of the securities offered hereby will be passed upon for us by Latham & Watkins LLP. Faegre Drinker Biddle & Reath LLP, is counsel to the Placement Agent in connection with this offering.

EXPERTS

The consolidated financial statements of Westport Fuel Systems as of December 31, 2025 and 2024 and for the years ended December 31, 2025 and 2024, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2025, have been incorporated by reference herein in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

KPMG LLP have confirmed with respect to us that they are independent within the meaning of the relevant rules and related interpretations prescribed by the relevant professional bodies in Canada and any applicable legislation or regulations and also that they are independent accountants with respect to us under all relevant U.S. professional and regulatory standards.

WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE

Available Information

We have filed with the SEC a registration statement on Form F-3 under the Securities Act, of which this prospectus supplement forms a part. The rules and regulations of the SEC allow us to omit from this prospectus supplement and the accompanying prospectus certain information included in the registration statement. For further information about us and the securities we are offering under this prospectus supplement, you should refer to the registration statement and the exhibits and schedules filed with the registration statement. With respect to the statements contained in this prospectus supplement and the accompanying prospectus regarding the contents of any agreement or any other document, in each instance, the statement is qualified in all respects by the complete text of the agreement or document, a copy of which has been filed as an exhibit to the registration statement.

We file reports and other information with the SEC. The SEC maintains a website that contains reports and information statements and other information about issuers, such as us, who file electronically with the SEC. The address of that website is https://www.sec.gov. As a foreign private issuer, we are exempt from, among other things, the rules under the Exchange Act prescribing the furnishing and content of proxy statements and our officers, directors and principal shareholders are exempt from the reporting and short-swing profit recovery provisions contained in Section 16 of the Exchange Act.

Our website address is www.westport.com. The information on, or accessible through, our website is not part of, and is not incorporated into, this prospectus supplement or the accompanying prospectus and should not be considered part of this prospectus supplement or the accompanying prospectus.

Incorporation by Reference

The SEC’s rules allow us to “incorporate by reference” information into this prospectus supplement, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is deemed to be part of this prospectus supplement and the accompanying prospectus, and subsequent information that we file with the SEC will automatically update and supersede that information. Any statement contained in a previously filed document incorporated by reference will be deemed to be modified or superseded for purposes of this prospectus supplement and the accompanying prospectus to the extent that a statement contained in this prospectus supplement or the accompanying prospectus modifies or replaces that statement.

We incorporate by reference our documents listed below and any future filings made by us with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act between the date of this prospectus supplement and the termination of the offering of the securities described in this prospectus supplement. We are not, however, incorporating by reference any documents or portions thereof, whether specifically listed below or filed in the future, that are not deemed “filed” with the SEC.

This prospectus supplement and the accompanying prospectus incorporate by reference the documents set forth below that have previously been filed with the SEC:

We incorporate by reference the following information or documents that we have filed with the SEC:

We are also incorporating by reference all subsequent annual reports filed on Form 20-F, Form 40-F or Form 10-K and all subsequent filings on Forms 10-Q and 8-K (if any) filed by us pursuant to the Exchange Act prior to the termination of the offering made by this prospectus. We may also incorporate by reference any Form 6-K that is submitted to the SEC after the date of the filing of the registration statement of which this prospectus supplement and the accompanying prospectus forms a part and before the date of termination of any offering hereunder. Any such Form 6-K that we intend to so incorporate shall state in such form that it is being incorporated by reference into this prospectus. In all cases, you should rely on the later information over different information included in this prospectus supplement or any accompanying prospectus supplement.

You may request a free copy of any of the documents incorporated by reference in this prospectus supplement and the accompanying prospectus (other than exhibits, unless they are specifically incorporated by reference in the documents) by writing or telephoning us at the following address:

Westport Fuel Systems Inc.

1691 West 75th Avenue

Vancouver, British Columbia V6P 6P2

Telephone: (604) 718-2046

1,600,000 Common Shares

Pre-Funded Warrants to Purchase up to 3,254,369 Common Shares

3,254,369 Common Shares underlying the Pre-Funded Warrants

Prospectus Supplement

Craig-Hallum

June 22, 2026