ACHN 2018 Proxy Statement

PROPOSAL 1—ELECTION OF DIRECTORS Our Board of Directors is divided into three classes and currently consists of three Class I Directors (Kurt Graves, David I. Scheer and Frank Verwiel), three Class II Directors (Michael D. Kishbauch, Robert L. Van Nostrand and Nicole Vitullo), and three Class III Directors (Milind S. Deshpande, Jason S. Fisherman and Gary E. Frashier). One class is elected each year and members of each class hold office for three year terms. Our Board of Directors has set the number of directors to be eight as of May 31, 2018, and established that Class III of the Board of Directors shall thereupon consist of two directors. The Class I, Class II and Class III Directors will serve until the annual meeting of stockholders to be held in 2019, 2020 and 2018, respectively, and until their respective successors are elected and qualified. At the annual meeting, Class III directors will stand for reelection. The persons named in the enclosed proxy card will vote to elect Drs. Deshpande and Fisherman as Class III Directors unless you indicate on your proxy that your shares should be withheld from one or more of the nominees. Each of the nominees is currently a member of our Board of Directors. If they are elected, Drs. Deshpande and Fisherman will each hold office until our annual meeting of stockholders in 2021 and until his or her respective successor is duly elected and qualified. Each of the nominees has indicated their willingness to serve, if elected; however, if any nominee should be unable to serve, the shares of common stock represented by proxies may be voted for a substitute nominee designated by the Board of Directors. There are no family relationships between or among any of our officers or directors. Below are the names, ages and certain other information for each member of the Board of Directors, including the nominees for election as Class III Directors. The information presented includes each director’s and nominee’s principal occupation and business experience for the past five years, and the names of other public companies of which he or she has served as a director during the past five years. The information presented below regarding the specific experience, qualifications, attributes and skills of each director and nominee led our Nominating and Corporate Governance Committee and our Board of Directors to conclude that he or she should serve as a director. In addition, we believe that all of our directors and nominees possess the attributes or characteristics described below under the heading “Director Nomination Process” that the committee expects of each director, including the candidate’s integrity, business acumen, knowledge of our business and industry, experience, diligence, age, lack of conflicts of interest, the ability to act in the interests of all stockholders and whether the candidate enhances the diversity of our Board of Directors. Information with respect to the number of shares of common stock beneficially owned by each director, directly or indirectly, as of February 28, 2018 appears above under the heading “Security Ownership of Certain Beneficial Owners and Management.” Information with respect to related party transactions, including those involving our directors, appears below under the heading “Certain Relationships and Related Transactions.” Nominees Whose Terms Expire in 2018 (Class III Directors) Milind S. Deshpande, Ph.D., age 61 . Dr. Deshpande has served as our Chief Executive Officer since May 2013, at which time he was also elected to our Board of Directors. Dr. Deshpande also served as our President from May 2013 to February 2018. Prior to that, he was our President of Research and Development and Chief Scientific Officer from October 2010 to May 2013. Prior to joining Achillion in September 2001, Dr. Deshpande was Associate Director of Lead Discovery and Early Discovery Chemistry at the Pharmaceutical Research Institute at Bristol-Myers Squibb, a pharmaceutical company, from 1991 to 2001, where he managed the identification of new clinical candidates to treat infectious and neurological diseases. From 1988 to 1991, he held a faculty position at Boston University Medical School. Dr. Deshpande is Chairman of the Board of Directors of Spero Therapeutics, Inc., a publicly traded biopharmaceutical company developing novel treatments for multi- drug resistant bacterial infections. Dr. Deshpande received his Ph.D. in Organic Chemistry from Ohio University, following his undergraduate education in India. 9