Kohona was the Secretary, Ministry of Foreign Affairs of Sri Lanka from 2006 to 2009. Ambassador Kohona was the Permanent Representative of Sri Lanka to the United Nations in New York from 2009 to 2015. During this period he was elected as the Chair of the UN GA Sixth Committee (Legal) in 2013.
Kohona held the position of Secretary, Ministry of Foreign Affairs of Sri Lanka between 2006 and 2009. He later became Ambassador to the United Nations in New York from 2009 to 2015 and was chosen as chair of the UN GA Sixth Committee (Legal) in 2013.