Brennan was a member of
U.S. National Under-18 Team for two seasons (2002–04). He played four seasons (2004–08) at
Boston College. In 2008 Breannan was named to the NCAA Championship All-Tournament Team. On April 16, 2010, Brennan was signed as a
free agent by the
Chicago Blackhawks, and he spent two seasons (2008–10) in the
AHL with Chicago's top farm team – the
Rockford IceHogs. He was invited to the
Toronto Maple Leafs 2010–11 Training camp, and on September 26, 2010, he was assigned to the Maple Leafs AHL affiliate, the
Toronto Marlies. After recording a career high 10 points, Brennan was signed to an AHL contract with the
Lake Erie Monsters for the
2011–12 season. Prior to the commencement of the season with the Monsters, Brennan was invited to and participated in the Monsters NHL affiliate,
Colorado Avalanche training camp. Upon his return to the Monsters, Brennan was a main fixture on the blueline appearing in a career high 74 games. A free agent into the
2012–13 season, and now classified as a veteran, Brennan belatedly signed a contract with the Florida Everblades of the ECHL on November 5, 2012. After 9 games with the Everblades, Brennan made a return to the AHL, when he was loaned to the Worcester Sharks on November 27, 2009. He made his eventful debut for the Sharks on November 30, against the
Portland Pirates. Brennan recorded 4 assists in 28 games before he was sideline by injury for the duration of the season. On June 21, 2013, after 310 games in the AHL, Brennan signed his first European deal; a one-year contract with the German club
Iserlohn Roosters of the
Deutsche Eishockey Liga (DEL). In the
2013–14 season with the Roosters, Brennan was a mainstay on the Blueline in appearing in 51 games and producing 1 goal and 7 points. After a second round exit in the post-season, Brennan was not retained by the Roosters and on September 30, 2014, Brennan accepted a try-out contract into the
2014–15 season, with Finnish club
Sport in the
Liiga. ==Career statistics==