Gleeson was born in Dublin, Ireland, before moving to Australia with his family as a child. Raised in Sydney, Australia, Gleeson attended Catholic Jesuit school St Aloysius' College representing the schools 1st XV rugby union team over 2 years and as captain in the latter and playing for the CAS 1st XV and the New South Wales 2nd XV. He went on to represent Australia at u/19 and u/21 (Captain).
Gleeson has enjoyed a distinct career, representing Northern Suburbs in the Sydney competition, the NSW Waratahs in the Super 12, LeinsterinIreland and finally most notably Ireland. His preferred position is as an openside flanker. Perhaps the highlight of his career was representing Ireland in the 2003 Rugby World Cup. He stands 1.86 m and his playing weight is 98 kg.
On numerous occasions George Hook has stated that Gleeson should start for Ireland as he feels he is their best openside flanker.
Gleeson retired from professional rugby at the end of the 07/08 season with a Magners League winners medal.
