Background
Costello's documented education and professional life are both based in Australia, which provides the national setting for the legal career described in this biography.
Costello's documented education and professional life are both based in Australia, which provides the national setting for the legal career described in this biography.
Costello studied law at the University of Western Australia, where the degrees of Bachelor of Jurisprudence and Bachelor of Laws were pursued. The university was established by the University of Western Australia Act 1911 as the first university in Western Australia. It opened to 184 students in 1913 and conferred its first degrees in law, science, arts, medicine and engineering in 1914.
The Faculty of Law was added in 1927 as the university's fourth faculty, and the university moved from its original Irwin Street site to the Crawley campus in 1932. Costello was admitted to the bar in Australia in 1983, marking the conclusion of this legal training.
Costello worked as a partner of Mallesons Stephen Jaques, an Australian commercial law firm recognized as one of the Big Six law firms in Australia. The firm's origins date to 1832, when a predecessor practice began in Western Australia, and its name drew on Sydney founders Montague Stephen and Alfred Jaques.
The Mallesons Stephen Jaques name was used from 1987. In 2012 the Australian firm joined the King & Wood Mallesons partnership, a group that also included the London firm SJ Berwin and the Chinese firm King & Wood. That international partnership was dissolved on 30 March 2026, and the Australian firm reverted to the Mallesons name.