Sir Ninian Martin Stephen (15 June 1923 – 29 October 2017) was an English-born Australian judge who served as the 20th governor-general of Australia, in office from 1982 to 1989.

During his early childhood, the three of them lived for periods in Switzerland (Geneva where he was christened and Montreaux), France (Paris, Cannes, and Saint-Cast-le-Guildo) and Germany (Wiesbaden), where Mylne took him to Nuremberg for the 1938 Reichsparteitag Grossdeutschland (5-12 September) which he photographed.

Following Japan's entry into World War II, Stephen completed full-time military training from 8 December 1941 to 15 February 1942 and was then posted to the 10th Field Regiment, Royal Australian Artillery, serving in Western Australia.

[9] Although Stephen was appointed to the High Court by a Liberal government, he proved not to be a traditional conservative upholder of states' rights.

In 1982 he was part of the majority that decided on a broad interpretation of the "external affairs power" of the Australian constitution in the Koowarta v Bjelke-Petersen case.

In 1987, his term was extended by 18 months as a mark of personal respect and also to allow Bill Hayden (to whom Hawke had promised the position) to leave politics at a time of his choosing.

[12] In 1989, Stephen became Australia's first Ambassador for the Environment[1] and, in his three-year term, was particularly energetic in working for a ban of mining in Antarctica.

From 1991 to 1995, he was a judge ad hoc of the International Court of Justice in the case East Timor (Portugal v. Australia) 1991–1995.

[11] Stephen later moved back into the legal field, becoming president of an arbitral tribunal constituted under Chapter 11 of the North American Free Trade Agreement (NAFTA), charged with the adjudication of an investment dispute between Mondev, a Canadian investor, and the United States.

[19] Stephen was made a Knight Commander of the Order of the British Empire (KBE) on 20 April 1972 "for distinguished services to the Law",[20] and sworn of the Privy Council in 1979.

In 1994 Queen Elizabeth II appointed him a Knight Companion of the Order of the Garter (KG), being the most recent Australian to be granted a knighthood in the personal gift of the monarch of Australia.

He therefore had the unusual distinction of holding six separate knighthoods and joined Lord Casey and Sir Paul Hasluck as one of the few Australian Knights Companion of the Order of the Garter.