He played seven test matches at lock for the Australian national rugby union team between 1989 and 1990, debuting against France in Strasbourg in November 1989, on the Wallabies 1989 tour of Europe.

[8]: 117, 166  Campese labelled FitzSimons' actions "a disgrace to the good name of rugby"[8]: 117  and asserted that "he was doing the game and its reputation enormous damage.

[11] He regularly appears on the Australian Foxtel program The Back Page, formerly hosted by rugby league journalist Mike Gibson and now Tony Squires.

For the Saturday edition of The Sydney Morning Herald, FitzSimons writes a column titled "The Fitz Files" which looks at all the happenings over the past seven days in sport.

[15] However, the Mike and Fitz Breakfast Show still trailed a long way behind the number one program on 2GB, hosted by FitzSimons' former coach Alan Jones.

At the University of Sydney he was a fellow of the Senate from 2009 to 2013,[30] as well as Pro-Chancellor,[31] a patron of The Russell Prize for Humour Writing, State Library of New South Wales, since 2015[32] and chairman of the Australian Republic Movement from 2015 to 2022.

He began by launching a petition in late 2017 on Change.org that reached approximately 220,000 signatures prior to the election as well as numerous editorial articles decrying the demolitions.

[36] On 5 December 2017, FitzSimons remarked on Twitter that the incumbent Gladys Berejiklian government could "bulldoze and rebuild three new stadiums, including Parra, for $3 billion—on no demand—or they can win the next election, but they can't do both.

"[37] On 23 March, Berejiklian and her coalition were easily returned to government, with political commentators suggesting that the issue did not resonate with the wider community of the state.

[38] The campaign had a minor success, however, as the government changed the original plan for a complete knock down rebuild of Stadium Australia, and instead would go ahead with a billion-dollar refurbishment.