[citation needed] He was appointed as a Circuit Court judge in April 2002.
He was appointed as a judge of the Tribunal of Inquiry into Certain Planning Matters and Payments in September 2002 and appointed chairman of the tribunal in July 2003.
In October 2014, he became a judge of the Court of Appeal.
[2][3] On 24 April 2018, the Government of Ireland decided to recommend Mahon for appointment as the new Ombudsman for the Defence Forces, for a three-year period with effect from 6 July 2018.
Mahon was recommended following an open competition run by the Public Appointments Service.