[1] He also served as an emeritus professor at Monash University and as the president of the International Association of Lawyers against Nuclear Arms.

Beginning his law practice in Colombo that went on until 1965, he was appointed Commissioner of Assize, holding the post until 1967 when he was called to the bench as a judge of the Supreme Court of Ceylon.

He retired from the Supreme Court in 1972 and moved to Australia where he assumed duties as Sir Hayden Starke Professor of Law, at Monash University in Victoria.

Weeramantry served on the Legal and Human Rights Advisory Board of the Genetics Policy Institute and the president of the International Association of Lawyers Against Nuclear Arms.

He was emeritus professor at Monash University, having previously served as Sir Hayden Starke's Chair of Law from 1972 to 1991.