Tommy Koh is currently an Emeritus Professor of Law at NUS; Ambassador-At-Large at the Ministry of Foreign Affairs; and Chairman of the International Advisory Panel of the Centre for International Law at the NUS.

He has served as Dean of the Faculty of Law of NUS, Singapore's Permanent Representative to the United Nations in New York, Ambassador to the United States of America, High Commissioner to Canada and Ambassador to Mexico. He was President of the Third UN Conference on the Law of the Sea. He was also the Chairman of the Preparatory Committee and the Main Committee of the UN Conference on Environment and Development (Earth Summit). He was the UN Secretary General’s Special Envoy to Russia, Estonia, Latvia and Lithuania. He was the founding Chairman of the National Arts Council, founding Executive Director of the Asia-Europe Foundation and former Chairman of the National Heritage Board. He was Singapore’s Chief Negotiator in negotiating an agreement to establish diplomatic relations between Singapore and China. He was also Singapore's Chief Negotiator for the US-Singapore Free Trade Agreement. He acted as Singapore's Agent in two legal disputes with Malaysia. He has chaired two dispute panels for the WTO. He is the Co-Chairman of the China-Singapore Forum and the Japan-Singapore Symposium.

Professor Koh has received awards from the Governments of Singapore, Chile, Finland, France,Japan, Netherlands, Spain and the United States. Professor Koh received the Champion of the Earth Award from UNEP and the inaugural President's Award for the Environment from Singapore. He was conferred with honorary doctoral degrees in law by Yale and Monash Universities. Harvard University conferred on him the Great Negotiator Award in 2014