Trevor John Riley was appointed as a Justice of the Supreme Court of the Northern Territory in 1999.

At the time of his appointment he was a member of the Northern Territory Bar Association having signed the Roll of Counsel in 1985. Justice Riley was a Northern Territory solicitor from 1974 to 1985.

Justice Riley was appointed as a Queen's Counsel in 1989. He was President of the Northern Territory Bar Association from 1993 to 1997 having been Vice President from 1989 to 1993. He was Junior Vice-President of the Australian Bar Association in 1993 to 1994.

Justice Riley is a former Vice-President of the Northern Territory Law Society and a former Councillor of that Society. He is a former member of the Legal Practitioners Complaints Committee, the Law Reform Committee, the Public Purposes Trust and the Legal Practitioners Admission Board. He is a former part-time lecturer at the Faculty of Law at the Northern Territory University and he is an occasional lecturer in Advocacy.