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 19, 2014

ENANTA PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

500 Arsenal Street, Watertown, Massachusetts 02472

(Address of principal executive offices and zip code)

(617) 607-0800

(Registrant’s telephone number, including area code)

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):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

On December 19, 2014, Enanta Pharmaceuticals, Inc. announced via press release the approval by the United States Food and Drug Administration, or FDA, regarding AbbVie’s hepatitis C treatment regimen containing paritaprevir, a compound developed in the collaboration between Enanta and AbbVie. A copy of Enanta’s press release is hereby furnished to the Commission and incorporated by reference herein as Exhibit 99.1.

(d) Exhibits

SIGNATURES

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.

EXHIBIT INDEX