A central defender, Fitzgerald's clubs included Wimbledon, Millwall and Colchester United.
Most of his games came for Wimbledon. He signed professional forms for them at the start of the 1987-88 season, but did not make his debut for nearly three years, coming on as a substitute against Tottenham Hotspur on 28 April 1990. He did not play again until the 1991-92 season, when he played in 36 out of 42 First Division games and helped the Dons secure a place in the new FA Premier League as well as their seventh successive campaign in the top flight. He remained a regular choice in defence for another three seasons, and when he lost his place in the 1995-96 season he was loaned to Sheffield United, and had a similar spell at Millwall in the 1996-97 campaign before finally departing Wimbledon on 29 July 1997 when a £50,000 fee took him to Division Two side Millwall on a permanent basis.
He managed 83 appearances for Millwall over the next three seasons, scoring once, as they failed to climb out of Division Two. Then came a four-year, 116-game, goalless spell at Colchester United, which again saw him remain in Division Two.
He finished his career at Brentford, playing an important role in their successful relegation battle in the 2003-04 season, though he rarely featured in the side during the 2004-05 under new manager Martin Allen and retired at the end of it. He remained at Brentford after his retirement as a player, landing the role of youth team coach.
Fitzgerald became caretaker manager of Brentford in November 2006 following the sacking of Leroy Rosenior. The position was made permanent on 21 December 2006. Despite a brief improvement in fortunes, Brentford were relegated from League One following a 3-1 defeat to Crewe. Fitzgerald's contract was terminated a day later on April 10, 2007.
It was announced on 30 July 2007 that Fitzgerald had joined Gillingham as youth team manager. On December 7, he rejoined Millwall in the same capacity.
Fitzgerald was also a Republic of Ireland B international.