Before being elected to the Court, Simma had served on the United NationsInternational Law Commission since 1996. From 1995 to 1997, he served as Dean of the University of Munich Faculty of Law. Prior to returning to his native Germany, he served as a Lecturer at the Hague Academy of International Law in the Netherlands, where he also served as Director of Studies in 1976 and 1982, and as Visiting Professor at the University of Michigan Law School during 1995. From 1987 to 1996, he served as a Member of the United Nations Committee on Economic, Social and Cultural Rights. From 1987 to 1992, he served as a Professor of Law at the University of Michigan Law School, and as a Visiting Professor in 1986. From 1984 to 1985, he served as a Visiting Professor at the University of Siena in Italy. He served as a Lecturer for International Law for the German Federal Foreign Ministry's Training Centre for Junior Diplomats. He received doctorate honoris causa from the University of Macerata, Italy in 2006. He is member of the advisory board of the Goettingen Journal of International Law.
Simma's term on the court expired on 5 February 2012; he was not a candidate for re-election.