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): February 5, 2015

ACTAVIS plc

(Exact Name of Registrant as Specified in Charter)

1 Grand Canal Square, Docklands

Dublin 2, Ireland

(Address of Principal Executive Offices)

(862) 261-7000

(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):

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On February 5, 2014, the Board of Directors (the “Board”) of Actavis plc (“Actavis”) voted to reduce the size of the Board from fourteen to twelve directors effective upon the earlier of the closing (the “Closing”) of Actavis’ acquisition of Allergan, Inc. (“Allergan”) and Actavis’ 2015 annual general meeting of shareholders (the “2015 Annual Meeting”).

In order to effectuate the reduction in the size of the Board and accommodate the appointment of two members of the Allergan board of directors to the Board at the Closing, as contemplated by the merger agreement entered into by Actavis and Allergan, each of Tamar D. Howson, John A. King, Jiri Michal and Andrew L. Turner will resign from the Board, in each case effective upon the earlier of the Closing and the 2015 Annual Meeting. The selection of the Allergan directors to be appointed to the Board at the Closing is ongoing.

The decision of each of Ms. Howson and Messrs. King, Michal and Turner to resign from the Board was not the result of any disagreement with Actavis on any matter relating to its operations, policies or practices.

Actavis Cautionary Statement Regarding Forward-Looking Statements

Statements contained in this communication that refer to Actavis’ estimated or anticipated future results, including estimated synergies, or other non-historical facts are forward-looking statements that reflect Actavis’ current perspective of existing trends and information as of the date of this communication. Forward looking statements generally will be accompanied by words such as “anticipate,” “believe,” “plan,” “could,” “should,” “estimate,” “expect,” “forecast,” “outlook,” “guidance,” “intend,” “may,” “might,” “will,” “possible,” “potential,” “predict,” “project,” or other similar words, phrases or expressions. Such forward-looking statements include, but are not limited to, statements about the benefits of the Allergan acquisition, including future financial and operating results, Actavis’ or Allergan’s plans, objectives, expectations and intentions and the expected timing of completion of the transaction. It is important to note that Actavis’ goals and expectations are not predictions of actual performance. Actual results may differ materially from Actavis’ current expectations depending upon a number of factors affecting Actavis’ business, Allergan’s business and risks associated with acquisition transactions. These factors include, among others, the inherent uncertainty associated with financial projections; restructuring in connection with, and successful closing of, the Allergan acquisition; subsequent integration of the Allergan acquisition and the ability to recognize the anticipated synergies and benefits of the Allergan acquisition; the ability to obtain required regulatory approvals for the transaction (including the approval of antitrust authorities necessary to complete the acquisition), the timing of obtaining such approvals and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the transaction; the ability to obtain the requisite Allergan and Actavis shareholder approvals; the risk that a condition to closing of the Allergan acquisition may not be satisfied on a timely basis or at all; the failure of the proposed transaction to close for any other reason; risks relating to the value of the Actavis shares to be issued in the transaction; the anticipated size of the markets and continued demand for Actavis’ and Allergan’s products; the impact of competitive products and pricing; access to available financing (including financing for the acquisition or refinancing of debt) on a timely basis and on reasonable terms; the risks of fluctuations in foreign currency exchange rates; the risks and uncertainties normally incident to the pharmaceutical industry, including product liability claims and the availability of product liability insurance on reasonable terms; the difficulty of predicting the timing or outcome of pending or future litigation or government investigations; periodic dependence on a small number of products for a material source of net revenue or income; variability of trade buying patterns; changes in generally accepted accounting principles; risks that the carrying values of assets may be negatively impacted by future events and circumstances; the timing and success of product launches; the difficulty of predicting the timing or outcome of product development efforts and regulatory agency approvals or actions, if any; market acceptance of and continued demand for Actavis’ and Allergan’s products; costs and efforts to defend or enforce intellectual property rights; difficulties or delays in manufacturing; the availability and pricing of third party sourced products and materials; successful compliance with governmental regulations applicable to Actavis’ and Allergan’s facilities, products and/or businesses; changes in the laws and regulations affecting, among other things, pricing and reimbursement of pharmaceutical products; changes in tax laws or interpretations that could increase Actavis’ consolidated tax liabilities; the loss of key senior management or scientific staff; and such other risks and uncertainties detailed in Actavis’ periodic public filings with the Securities and Exchange Commission, including but not limited to Actavis’ Annual Report on Form 10-K for the year ended December 31, 2013, as amended by Actavis’ Current Reports on Form 8-K filed on May 20, 2014 and December 5, 2014, Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2014, in Warner Chilcott Limited’s Registration Statement on Form S-4 effective as of October 15, 2014, and the related prospectus, and from time to time in Actavis’ other investor communications. Except as expressly required by law, Actavis disclaims any intent or obligation to update or revise these forward-looking statements.

Important Information for Investors and Shareholders

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. In connection with the proposed merger between Actavis and Allergan, Actavis has filed with the Securities and Exchange Commission (the “SEC”) a registration statement on Form S-4, including Amendment No. 1 thereto, that contains a joint proxy statement of Actavis and Allergan that also constitutes a prospectus of Actavis. The registration statement was declared effective by the SEC on January 26, 2015. Each of Actavis and Allergan

commenced mailing the joint proxy statement/prospectus to its shareholders or its stockholders on January 28, 2015. INVESTORS AND SECURITY HOLDERS OF ACTAVIS AND ALLERGAN ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS THAT HAVE BEEN FILED OR WILL BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders are able to obtain free copies of the registration statement and the joint proxy statement/prospectus and other documents filed with the SEC by Actavis and Allergan through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed with the SEC by Actavis are available free of charge on Actavis’ internet website at www.Actavis.com or by contacting Actavis’ Investor Relations Department at (862) 261-7488. Copies of the documents filed with the SEC by Allergan are available free of charge on Allergan’s internet website at www.Allergan.com or by contacting Allergan’s Investor Relations Department at (714) 246-4766.

Participants in the Merger Solicitation

Actavis, Allergan, their respective directors and certain of their executive officers and employees may be considered participants in the solicitation of proxies in connection with the proposed transaction. Information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of the Actavis and Allergan shareholders in connection with the proposed merger is set forth in the joint proxy statement/prospectus. Information about the directors and executive officers of Allergan is set forth in its proxy statement for its 2014 annual meeting of stockholders, which was filed with the SEC on March 26, 2014 and certain of its Current Reports on Form 8-K. Information about the directors and executive officers of Actavis is set forth in Actavis’ proxy statement for its 2014 annual meeting of stockholders, which was filed with the SEC on March 28, 2014 and certain of Actavis’ Current Reports on Form 8-K. Additional information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, is contained in the joint proxy statement/prospectus filed with the above-referenced registration statement on Form S-4 and other relevant materials to be filed with the SEC when they become available.

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.

Date: February 10, 2015