His career as a Foreign Service officer began in 1970. He has held several positions in the Ministry of Foreign Affairs including as director general of multilateral affairs (1997-2000) and secretary of the Ministry of Foreign Affairs (2003-2004). During his career, he served as permanent representative of Sri Lanka to the United Nations in Geneva (1992-1997), during which period he was concurrently accredited to the Holy See and as permanent representative of Sri Lanka to the UN in Vienna.

Later he served as Sri Lanka’s ambassador to the People’s Republic of China (2000-2003), during which assignment he was concurrently accredited as ambassador to the People’s Republic of Mongolia and the Democratic People’s Republic of Korea. Following the signing of the Ceasefire Agreement in 2002, Ambassador Goonetilleke was appointed as director general of the Secretariat for Coordinating the Peace Process and functioned as a member of the government negotiating team. He also served as acting permanent representative of Sri Lanka to the UN in New York (2004-2005) and ended his diplomatic career as ambassador to the United States of America (2005-2008).

In August 2008, he was appointed chairman of the Sri Lanka Institute of Tourism and Hotel Management in August 2008 and later served as chairman of the Sri Lanka Tourism Development Authority and Sri Lanka Tourism Promotion Bureau from November and December 2008, respectively, to February 2010. Since May 2010, he has served as a director of several companies associated with Mercantile Merchant Bank Limited and chairperson of the Pathfinder Foundation. He holds a degree in history and a diploma in international relations.