He obtained a Bachelor of Laws from the University of Adelaide and was admitted to the South Australian Bar in 1950. He practised as a barrister and solicitor in the firm of Thomson & Co until 1970 when he was appointed as a Judge of the Local and District Criminal Court of South Australia. He was appointed as a Queen's Counsel in 1967. Current Judge Dean Mildren was his Articled Clerk from 1966 - 1968.
He was appointed as a Judge of the Supreme Court of the Northern Territory on 1 May 1974 and became the second resident Judge (with William Forster). Later that year Dick Ward would be appointed as the third resident Judge. When the Federal Court of Australia was established in 1976 he was appointed as a Judge of that Court and held both that commission and the Supreme Court commission concurrently.[3]
After Sir William Forster retired on 7 February 1985 he was appointed as acting Chief Justice until his retirement on 11 September 1985 when Kevin O'Leary succeeded him.
He relocated to Perth, Western Australia and resigned his commission as Federal Court Judge in 1986 to take up the position of Royal Commissioner for the Royal Commission into Aboriginal Deaths in Custody, which ran from 1987 to 1991, with hearings finishing in 1989. On 1 July 1989 he was appointed as Administrator of the Northern Territory, a position he held until 4 December 1992.[3]
As Administrator he opened the new Supreme Court Building in 1991. At that time he was patron of 74 organisations. He was Deputy Prior of the Order of St John, Chief Scout in the Northern Territory and chairman of the Forum for Indigenous Studies at the North Australia Research Unit. He was also the second honorary colonel of Norforce.[citation needed]
Muirhead presided over Australia's most famous criminal murder trial, that of R v Chamberlain & Chamberlain, when Lindy and Michael Chamberlain were charged with the murder of their daughter Azaria. He sentenced Lindy to life imprisonment on 29 October 1982.[4] In the 1988 film Evil Angels, which was based on the events surrounding the trial, Muirhead was portrayed by the actor Charles 'Bud' Tingwell.
