He successfully defended what was then the longest civil jury trial in Australian legal history, when he appeared as leading counsel for Channel 9 in a 13-week defamation trial, in which Sir Leslie Thiess sought damages from Channel 9 following a report broadcast on that network that he had bribed the Premier of Queensland, Joh Bjelke-Petersen.

That view was most trenchantly expressed in his lengthy dissent in New South Wales v Commonwealth, a case concerned with the constitutional validity of the Howard government's WorkChoices legislation.

[9] Callinan's judgment in that case is the longest in the history of the High Court, containing approximately 55,000 words and running for 165 pages.

[10] There is nothing in the text or the structure of the Constitution to suggest that the Commonwealth's powers should be enlarged, by successive decisions of this Court, so that the Parliament of each State is progressively reduced until it becomes no more than an impotent debating society.

While on the High Court he spoke out against the death penalty (which has been abolished in Australia), most notably in a speech to the 2005 Law Asia conference.

In my experience, the phenomenon of human fallibility is irrefutable, and, in my view, must be accorded primacy when weighing the arguments in favour of, and against, the death penalty ...

The fallibility of the criminal justice system, the inability to prove the deterrence theory, and my personal revulsion of state sponsored execution of human beings support the abolition of capital punishment.Callinan was described by Justice Susan Kenny of the Federal Court of Australia in article published in 2003 as 'the leading' exponent of the 'prudential ethical' method of constitutional adjudication during the 2002 term.

Justice Kenny defined the 'prudential ethical mode' as 'a constitutional argument that relies on economic, social or political considerations attending the case ... a self-consciously evaluative style'.

[17] Callinan's broader legal philosophy was considered by Professor Michael Bryant in a 2008 article published in the University of Queensland Law Journal.

Bryant concluded that in his judgments on private law, Callinan 'showed a strong preference for achieving corrective justice, and a corresponding reluctance to take into account arguments based on considerations of distributive justice ... based on clearly held and expressed views on the proper limits of the appellate judicial role'.

[18] Immediately upon his retirement from the High Court, Callinan was called back into public service through his appointment[19] to conduct a Commission of Inquiry into the outbreak of equine influenza in Australia.

[24] In March 2015, the New Zealand Government chose Callinan to review once again David Bain's claims for compensation for wrongful conviction and imprisonment after rejecting an earlier report by Canadian judge Ian Binnie.

[27] In 2016, Callinan was appointed by the Deputy Premier of New South Wales Troy Grant MP to conduct a review of the effectiveness of the Sydney lockout laws, which restrict the sale of alcohol and the admission of patrons to some alcohol-serving venues.

[39] Apart from his judicial writings he is a novelist (The Lawyer and the Libertine, The Missing Masterpiece, The Coroner's Conscience, Appointment at Amalfi, After the Monsoon, The Russian Master, Betrayals and The Only Case) and a playwright (Brazilian Blue, The Cellophane Ceiling, The Acquisition[40] and A Hero's Funeral[41]).

In 2003, Justice Callinan was appointed a Companion of the Order of Australia (AC) for his services to the law, arts and the community.