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): January 3, 2013

INSULET CORPORATION

(Exact name of registrant as specified in its charter)

9 Oak Park Drive

Bedford, Massachusetts 01730

(Address of Principal Executive Offices, including Zip Code)

Registrant’s telephone number, including area code: (781) 457-5000

Not Applicable

(Former Name or 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 (see General Instruction A.2. below):

On January 3, 2013, Insulet Corporation (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Canaccord Genuity Inc. (the “Underwriter”), for the sale by the Company to the Underwriter of 4,100,000 shares of common stock, par value $0.001 per share (the “Firm Shares”). The Firm Shares will be sold to the Underwriter pursuant to the Underwriting Agreement at a price of $19.77 per share. The offering is expected to close on or about January 9, 2013, subject to customary closing conditions. The Company has granted the Underwriter a 30-day option to purchase an additional 615,000 shares of common stock (together with the Firm Shares, the “Shares”).

The Underwriting Agreement contains customary representations, warranties and covenants by the Company. It also provides for customary indemnification by each of the Company and the Underwriter for losses or damages arising out of or in connection with the sale of the Shares.

The offering is being made pursuant to a registration statement on Form S-3 (File No. 333-172782) filed with the Securities and Exchange Commission (the “Commission”) on March 11, 2011, in the form in which it became effective on March 28, 2011 (the “Registration Statement”), the prospectus included in the Registration Statement and a final prospectus supplement relating to the Shares filed pursuant to Rule 424(b)(5) of the Securities Act on January 4, 2013.

A copy of the Underwriting Agreement is attached as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference, and the foregoing description of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Underwriting Agreement.

On January 3, 2013, the Company issued a press release announcing the sale of 4,100,000 shares of its common stock pursuant to the Underwriting Agreement. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information disclosed under this Item 7.01, including Exhibit 99.1 hereto, is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, nor shall it be incorporated by reference into any registration statement or other document pursuant to the Securities Act, except as expressly set forth in such filing.

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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.

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EXHIBIT INDEX

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