[3] Gleeson was admitted as a lawyer in 1989, and worked as an associate to Justice Trevor Morling of the Federal Court and then as a solicitor for Bush Burke & Company.
[2][3][4][5] Gleeson was appointed to the Federal Court by Attorney-General George Brandis on 15 April 2014, replacing retired Justice Dennis Cowdroy.
[5] Gleeson has sat on a number of high-profile cases, dismissing claims against the Australian Securities and Investments Commission brought by clients of Storm Financial that alleged that the regulator should have taken action to prevent their loss.
[12] In June 2019, Gleeson found in favour of Kimberly-Clark Australia in Australian Competition and Consumer Commission's (ACCC) case against them for the claim that "flushable wipes" were in fact safely flushable in Australia's sewerage system, saying that although they contributed to household sewerage system blockages in an unknown number of instances, even faecal matter and toilet paper contributed to those problems.
[13] On 28 October 2020, Prime Minister Scott Morrison and Attorney-General Christian Porter announced that Gleeson and Simon Steward would be appointed to the High Court of Australia to fill the vacancies caused by upcoming retirements of Geoffrey Nettle and Virginia Bell.