UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 24, 2017

ACHAOGEN, INC.

(Exact name of registrant as specified in its charter)

1 Tower Place, Suite 300

South San Francisco, CA 94080

(Address of principal executive offices, including Zip Code)

Registrant’s telephone number, including area code: (650) 800-3636

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 financing accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☒

Item 8.01 Other Events.

On May 24, 2017, Achaogen, Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Leerink Partners LLC, Cowen and Company, LLC and Stifel, Nicolaus & Company, Incorporated, as representatives (the “Representatives”) of the several underwriters named therein (collectively, the “Underwriters”), pursuant to which the Company agreed to issue and sell 5,000,000 shares (the “Shares”) of its common stock, par value $0.001 per share (“Common Stock”), to the Underwriters (the “Offering”). The Shares were sold at a public offering price of $22.50 per Share, and were purchased by the Underwriters from the Company at a price of $21.15 per Share. Under the terms of the Underwriting Agreement, the Company granted the Underwriters the option, for 30 days, to purchase up to 750,000 additional shares of Common Stock at the public offering price.

The Offering was made under a prospectus supplement and related prospectus filed with the Securities and Exchange Commission pursuant to the Company’s effective shelf registration statement on Form S-3 (Registration No. 333-217787).

On May 31, 2017, the Offering closed and the Company completed the sale and issuance of an aggregate of 5,000,000 shares of Common Stock. The Company received net proceeds from the Offering of approximately $105.4 million, after deducting the Underwriters’ discounts and commissions and estimated offering expenses payable by the Company. As of March 31, 2017, the Company had cash, cash equivalents and short-term investments of approximately $132.0 million and, after giving effect to the issuance and sale of shares of Common Stock in the Offering, had approximately $237.4 million in cash, cash equivalents and short-term investments.

Pursuant to the Underwriting Agreement, the Company agreed to indemnify the Underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended, or to contribute to payments that the Underwriters may be required to make because of such liabilities. The Company and the Company’s directors and executive officers (and certain of their affiliated stockholders) also agreed not to sell or transfer any Common Stock for 60 days after May 24, 2017 without first obtaining the written consent of the Representatives on behalf of the Underwriters, subject to certain exceptions as described in the prospectus supplement.

A copy of the Underwriting Agreement is attached as Exhibit 1.1 hereto and is incorporated herein by reference. The foregoing descriptions of the Underwriting Agreement and lock-up arrangements do not purport to be complete and are qualified in their entirety by reference to such exhibit.

A copy of the opinion of Latham & Watkins LLP relating to the validity of the securities issued in the Offering is filed herewith as Exhibit 5.1.

(d) Exhibits.

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 hereunto duly authorized.