After his Senior year of High School with Tabor Academy defenseman Rich Brennan was drafted by the Quebec Nordiques but elected to pursue an education and collegiate hockey before embarking on his professional career. Brennan went to play at Boston University and was njamed to the Hockey East First All-Star Team and the NCAA East Second All-American Team for his efforts in 1994.
In 1995 he began a pro career that would be spent as a journeyman depth defenseman. Though most of his hockey would be played in the American Hockey League, Brennan also earned several short stints in the NHL as well. He split his first season between the Colonial League's Branford Smoke and the AHL's Cornwall Aces. In 1996-97 he spent the bulk of his season in the minors with the Hershey Bears but he was called up to the NHL for a two game audition.
The Nordiques and moved to Colorado and become the Avalanche by this point and they suited the 6'2 blue liner up for two games in which he was held scoreless. At season's end Brennan became a free agent and inked a deal with the San Jose Sharks.
The Sharks gave Brennan a longer look in the big leagues by inserting him in their line up for 11 games and he responded with a goal and two assists. After also playing 42 games for their farm club, Brennan was traded by the Sharks to the New York Rangers in exchange for goaltender Jason Muzzatti and finished his year with their AHL affiliate, the Hartford Wolf Pack.
With the Rangers in 1998, Brennan enjoyed his longest stint in the NHL by playing 24 games on Broadway and scoring a goal and three assists.
Just prior to the 1999-00 campaign, Brennan was claimed by the Los Angeles Kings and spent all but two games over the next two seasons toiling for their minor league club. In the summer of 2001 Brennan signed a deal that would bring him to his fifth NHL club, the Nashville Predators.
Brennan got into four games with the Predators, but spent the rest of his time back in the AHL with the Milwaukee Admirals before a December 18 trade sent him back to the Los Angeles Kings.