The Honourable Justice Callaghan was admitted as a barrister in 1986 and worked as a Crown Prosecutor with the Commonwealth Office of the Director of Public Prosecutions in Brisbane and in the Australian Capital Territory.
In 1991 his Honour moved to the Queensland ODPP and worked in the role of Senior Crown Prosecutor until he joined the private Bar in 1995. Justice Callaghan’s first defence brief was as junior counsel in the trial of R v Ivan Milat. In 2004 his Honour was appointed (and in 2013 he remained) Senior Counsel.
At the private Bar, his Honour principally practised in criminal and administrative law. High profile cases in which he appeared involved movie stars, millionaires and politicians. Some notable pro bono work included homeless people, indigenous families and community
organisations. At his swearing in he was described by the President of the Bar Association as having been a “true jury whisperer”. In addition to his trial and appellate practice, Justice Callaghan appeared as Senior Counsel Assisting in the Queensland Floods Commission of Inquiry and the Royal Commission into the Protection and Detention of Children in the Northern Territory.
His Honour served on the Bar Association of Queensland (BAQ) Council, on the editorial committee of the Bar News, and as a BAQ Ethics Counsellor. He also served on the Board of Legal Aid Queensland. At the time of his appointment as a judge, Justice Callaghan was
chair of the Criminal Law Committee of the Australian Bar Association. He continues to be an author of the authoritative text “Carter’s Criminal Law of Queensland”.
Justice Callaghan was appointed a judge of the Supreme Court of Queensland on 10 February 2020 and member of the Mental Health Court of Queensland on 5 August 2025.