He lived at Kilminchy Castle, Portlaoise, and Mount Offaly, County Kildare.
He was elected to the Irish House of Commons for Boyle on 21 October 1763 and sat until his death.
He married firstly, Margaret, daughter of James King, 4th Baron Kingston, of Mitchelstown Castle and his first wife Elizabeth Meade, daughter of Sir John Meade, 1st Baronet.
[citation needed] He married, secondly, Mary, daughter and heiress of Fairfax Mercer, of Fair Hill, County Louth.
In 1776 Fitzgerald was shot in a duel with his daughter's father-in-law, Edward King, 1st Earl of Kingston.