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): December 11, 2014

MEI Pharma, Inc.

(Exact name of registrant as specified in its charter)

11975 El Camino Real, Suite 101, San Diego, California 92130

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (858) 792-6300

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 (see General Instruction A.2. below):

On December 11, 2014 MEI Pharma, Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Merrill Lynch, Pierce, Fenner & Smith Incorporated, as representative of the several underwriters named therein (collectively, the “Underwriters”), relating to the issuance and sale of 10,000,000 shares of the Company’s common stock, par value $0.00000002 per share (“Common Stock”), at a public offering price of $4.00 per share. Pursuant to the Underwriting Agreement, the Company granted the Underwriters a 30-day option to purchase up to an additional 1,500,000 shares of Common Stock.

The net proceeds to the Company from this offering, including the proceeds from the underwriters’ exercise of the option to purchase additional shares, are expected to be approximately $43.0 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. The offering is expected to close on or about December 17, 2014, subject to customary closing conditions.

The offering is being made pursuant to the Company’s effective registration statement on Form S-3 (Registration Statement No. 333-195122) previously filed with and declared effective by the Securities and Exchange Commission (the “SEC”) and a prospectus supplement and accompanying prospectus filed with the SEC.

The Underwriting Agreement contains customary representations, warranties and agreements by the Company, customary conditions to closing, indemnification obligations of the Company and the Underwriters, including for liabilities under the Securities Act of 1933, as amended, other obligations of the parties and termination provisions. The representations, warranties and covenants contained in the Underwriting Agreement were made only for 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.

The foregoing description of the Underwriting Agreement is not complete and is qualified in its entirety by reference to the full text of the Underwriting Agreement, a copy of which is filed as Exhibit 1.1 to this report and which is incorporated by reference herein. A copy of the opinion of Morgan, Lewis & Bockius LLP relating to the legality of the issuance and sale of the Shares in the offering is attached as Exhibit 5.1 to this report.

On December 12, 2014, the Company issued a press release announcing the pricing of the offering, a copy of which is attached as Exhibit 99.1 to this report and is incorporated herein by reference.

(d) Exhibits.

SIGNATURE

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

Dated: December 17, 2014

Index to Exhibits