SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Rule 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): June 6, 2018

Zymeworks Inc.

(Exact name of registrant as specified in its charter)

(604) 678-1388

(Registrant’s telephone number, including area code)

Not Applicable

(Former name of former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☑

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☑

On June 6, 2018, Zymeworks Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Citigroup Global Markets Canada Inc. and Wells Fargo Securities Canada, Ltd., as representatives of the several underwriters named in Schedule II thereto (the “Underwriters”), relating to the issuance and sale of 5,400,000 of the Company’s common shares, without par value (the “Offered Shares”), at a price to the public of US$15.75 per share (the “Offering”), which will result in approximately US$79 million of net proceeds to the Company after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. In addition, the Company granted the Underwriters a 30-day option to purchase up to 810,000 additional common shares to cover over-allotments, if any. The Offering is expected to close on or about June 11, 2018, subject to customary closing conditions.

The Offering is being made pursuant to the Company’s effective shelf registration statement on Form F-10 (No. 333-224623) previously filed with the Securities and Exchange Commission (“SEC”), including the prospectus, dated May 24, 2018, and the prospectus supplement, dated June 6, 2018.

The Underwriting Agreement contains customary representations, warranties and agreements by the Company, conditions to closing, indemnification obligations of the Company and the Underwriters, including for liabilities under the Securities Act of 1933, as amended, and other obligations of the parties and termination provisions. The representations, warranties and covenants contained in the Underwriting Agreement were made only for the purposes of such agreement and as of specific dates, were solely for the benefit of the parties to such agreement and may be subject to limitations agreed upon by the contracting parties. In addition, pursuant to the terms of the Underwriting Agreement, the Company and the executive officers and directors of the Company have entered into “lock-up” agreements with the Underwriters, which generally prohibit the sale, transfer or other disposition of common shares of the Company or securities convertible into, exchangeable for, exercisable for or repayable with common shares of the Company for a 90-day period with respect to the Company and a 60-day period with respect to the Company’s executive officers and directors, subject to certain exceptions.

The foregoing is only a brief description of the terms of the Underwriting Agreement and the transactions contemplated thereby, and is qualified in its entirety by reference to the Underwriting Agreement that is filed as exhibit 99.1 hereto.

On June 6, 2018, Zymeworks issued a press release announcing the filing of a preliminary prospectus supplement in connection with the Offering, which was filed with the Canadian securities regulatory authorities in Canada on the System for Electronic Document Analysis and Retrieval (“SEDAR”) at www.sedar.com. Additionally, on June 6, 2018, Zymeworks issued a press release announcing the pricing of the Offering, which was filed with the Canadian securities regulatory authorities in Canada on SEDAR. Copies of these press releases are attached as exhibits 99.2 and 99.3, hereto.

The information provided under this Item (including Exhibits 99.2 and 99.3, attached hereto) shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

In reviewing the Underwriting Agreement included as exhibit 99.1 to this report, please remember that it is included to provide you with information regarding its terms and is not intended to provide any other factual or disclosure information about the Company or the other parties to the Underwriting Agreement. The Underwriting Agreement contains representations and warranties by each of the parties to the Underwriting Agreement. These representations and warranties have been made solely for the benefit of the other parties to the Underwriting Agreement and:

Accordingly, these representations and warranties may not describe the actual state of affairs as of the date they were made or at any other time. Additional information about the Company may be found elsewhere in this report and the Company’s other public filings, which are available without charge through the SEC’s website at http://www.sec.gov.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.