Barrett was admitted as a solicitor in New South Wales on 17 March 1967. He was an articled clerk with Allen Allen & Hemsley, a year behind William Gummow and a year ahead of John Lehane. On admission he became an employed solicitor and made partner in 1971. From 1987 to 1989 he was their resident partner in London. Barrett was appointed as a part-time member of the Companies and Securities Law Review Committee between 1983 and 1987. In 1991 Barrett left Allens to become Group Secretary and General Counsel for Westpac Banking Corporation which had been one of his clients at Allens. From 1991 he was a part-time member of the Commonwealth Companies and Securities Advisory Committee and convenor of its legal committee. In May 1995 Barrett became a partner at Mallesons Stephen Jaques where he practised until his commission as a judge of the Supreme Court of New South Wales in 2001. In 1997 he was appointed Deputy Chairman of the Australian Stock Exchange Appeal Tribunal and then Chairman in January 1998. As a corporate and securities law specialist he was involved in several important and complex Australian corporate cases: the 1995 Westpac Challenge Bank merger, the NRMA insurance demutualisation, Comalco's takeover of Rio Tinto and the Australian Stock Exchange demutualisation and self-listing which was a world first. Barrett has been noted for his commitment to legal education. From 1973 to 1974 and from 1976 to 1987, he was a part-time lecturer at the Sydney Law School of The University of Sydney. He was also a consultant to the Legal Workshop, Australian National University from 1973 to 1977. He chaired the Legal Qualifications Committee of the New South Wales Legal Practitioners Admission Board which he had joined in 2002. Barrett has been a member of the editorial board of the Company and Securities Law Journal since it began publication in 1982. He was the general editor of Robson's Annotated Corporations Legislation from 2010 to 2019, and is a member of the advisory board of Practical Law Australia and an assistant editor of the New South Wales Law Reports. Barrett was sworn in as a Justice of the Supreme Court of New South Wales on 19 March 2001. In 2012 he was commissioned as a Judge on the New South Wales Court of Appeal. Barrett retired from both positions with effect from 20 April 2015. On 10 June 2019 he was appointed an Officer in the General Division of the Order of Australia for distinguished service to the law, and to the judiciary, particularly in the area of corporations law and legislation.
Personal life
On the 1 August 1970 he married Susan, the daughter of Mervyn G. and Dorothy M. Campbell. They have two sons. He has sung with the Sydney Philharmonic Choir including as one of their twelve hundred at the Opening Ceremony of the Sydney Olympic Games.
