He was emeritus professor at Monash University, having previously served as Sir Hayden Starke's Chair of Law from 1972 to 1991. A former Lecturer and Examiner at the Colombo Law College, he was a member of the Council of Legal Education in Ceylon. Weeramantry has also served as a visiting Professor at Harvard University (2000), University of Hong Kong (1989), University of Florida (1984), University of Colombo (1981), University of Papua New Guinea (1981), University of Stellenbosch (1979) and University of Tokyo (1978). He was an honorary member of Advisory Committee of Environmental Law Institute and Chairman of the International Council, Institute of Sustainable Development, McGill University.