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): April 4, 2013

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 April 4, 2013, MEI Pharma, Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Stifel, Nicolaus & Company, Incorporated and Cowen and Company, LLC, as representatives of the several underwriters named therein (collectively, the “Underwriters”), relating to the issuance and sale of 2,030,000 shares (the “Shares”) of the Company’s common stock, par value $0.00000002 per share (“Common Stock”). The price to the public for the offering is $7.50 per Share. The Underwriters have agreed to purchase the Shares from the Company pursuant to the Underwriting Agreement at a price of $7.05 per Share. The net proceeds to the Company from this offering are expected to be approximately $14.1 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. The offering is expected to close on or about April 10, 2013, subject to customary closing conditions.

The offering is being made pursuant to the Company’s effective shelf registration statement on Form S-3 (Registration Statement No. 333-173266) 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.

A copy of a press release announcing the offering that was issued by the Company on April 5, 2013 is attached as Exhibit 99.1 to this report and is incorporated herein by reference.

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: April 10, 2013

Index to Exhibits