Lancelot John Priestley served as a Justice of the Supreme Court of the Northern Territory from 1992 - 2006.

Justice Priestley was admitted to the New South Wales Bar in 1956 and practised under the former Chief Justice of New South Wales, Laurence Street. Justice Priestley was appointed as a Queen's Counsel in 1972.

Justice Priestley was a Judge of the Appeal Division of the Supreme Court of New South Wales in 1983 and served in that capacity until his retirement in 2001.

Justice Priestley has served as a Member of the New South Wales Supreme Court Library Committee from 1985 - 2001, was Chair of the New South Wales Barristers Admission Board and Solicitors Admission Board from 1989 - 1991. Justice Priestley was a member of the New South Wales Supreme Court Rules Committee from 1991 - 2001 and a member of the Chief Justice of New South Wales' Policy and Planning Committee from 1996 - 2001.