Born the son of Edward FitzGerald and his second wife, a daughter of Major Thomas Burton, FitzGerald was commissioned as an ensign in Captain Shee's independent company of foot, then based in Ireland, on 29 October 1793. Promoted to lieutenant in January 1794, he transferred to the 46th Regiment of Foot with the rank of captain on 31 October 1800. He subsequently transferred to the newly formed New Brunswick Fencibles on 9 July 1803 and was promoted to brevet major on 25 September 1803. After exchanging into the 60th Royal Americans with the substantive rank of major in 1809, he was promoted to lieutenant colonel on 25 July 1810.