Trevor captained St Mary’s College RFC to their only AIB League title in 2000. A very physical forward, he was a firm fans’ favourite at the south Dublin club. He began his career with Barnhall.

After leaving Leinster for Stade Toulousain, He subsequently went on to play in three back to back European Cup finals as part of the Stade Toulousin team, with two wins (Perpingnan 2003, Stade Français 2004) and one defeat (against Wasps 2004)

Trevor made his debut for the senior Ireland national rugby union team team in a 13-37 defeat against South Africa national rugby union team on June 13 1998 and went on to make 13 test appearances, including the 1999 Rugby World Cup.

Following retirement from professional rugby in 2007 Trevor and family have remained in Toulouse. The De Danu is widely considered one of the best sporting bars in Toulouse and is a firm favourite for Toulouse fans on match day. Additionally Trevor continues to write for the Irish Times in his article « Trevor Brennan Diaries » and appears on television as commentator for various rugby events including the 2007 Rugby World Cup.

In 2007 Brennan won the William Hill Irish Sports Book of the Year Award for his book Heart and Soul. The book, which was written with the assistance of Irish Times journalist Gerry Thornley, depicts Brennan from his time growing up in Leixlip and playing for Barnhall right through to his time at Toulouse where he won two European Cups.

In 2008 Trevor Brennan and rugby national fitness coach Mike McGurn, were part of the Ireland International rules football coaching staff in the International rules match series with Australia. Both Brennan and McGurn had played Gaelic Football in their youth and were invited by the Irish manager, Seán Boylan and the GAA to give their expertise from Rugby which would be useful in the game which is a compromise between Aussie Rules and Gaelic Football.

Trevor continues to actively support Rugby both here in Toulouse, and in Ireland. He is also actively involved in various sports related charity events and supports several charities including The Samaritans. One of Trevors main passions is to continue to provide the people of Toulosue and visitors to the city with real Irish hospitality, which the De Danu has become famous for.