From 1950 to 1953, Mahoney was educated at St Patrick's College, Silverstream, where he was proxime accessit to the dux in his final year.
[3] In 1978, Mahony was appointed to the bench as a stipendary magistrate (now called District Court judge) based in Auckland.
[4] Mahony retired as principal Family Court judge in 2004, and was succeeded in that role by Peter Boshier.
[6][7][8][9] Following his retirement from the Family Court, Mahony served as a member of the New Zealand Parole Board, and succeeded Anand Satyanand as chair of the confidential forum for former psychiatric patients.
[11] In the 2004 New Year Honours, he was appointed a Distinguished Companion of the New Zealand Order of Merit, for services to the Family Court.