In 1969, Mason was made a judge of the Supreme Court of New South Wales, where he sat as a member of the Court of Appeal. In the same year he was appointed by the Gorton Government to a three-year term on the council of the Australian National University. He served on the Supreme Court until 1972, when he was appointed to the bench of the High Court of Australia and received a knighthood (KBE). After fifteen years on the High Court, and following the retirement of Sir Harry Gibbs, in 1987 Mason was appointed Chief Justice; he retired in 1995 on reaching the constitutionally mandatory retirement age of 70.