他從1980年到1982年期間擔任[[聯合國海洋法公約|第三屆聯合國海洋法會議]]主席。

Lax and Sebenius present Koh and his efforts in getting the Convention passed, as an example of successful negotiating.<ref>David A. Lax and James K. Sebenius, "Thinking Coalitionally: Party Arithmetic, Process Opportunism, and Strategic Sequencing," in H. Peyton Young, ed. Negotiation Analysis. (Ann Arbor: University of Michigan Press, 1991), pp. 153–194.</ref> 1990 to 1992 he served as Chairman of the Main Committee of the [[地球高峰會|UN Conference on Environment and Development]], where he presided over the negotiations on [[21世紀議程|Agenda 21]]. He has also served as Singapore's ambassador to the United Nations and {{tsl|en|Singaporean Ambassador to the United States||the United States}}.