An inaugural squad member, Brennan served as Worsfold’s vice captain during the early 1990s. He was there for all of West Coast’s big moments: the inaugural win over Richmond, the lost Grand Final in 1991, the breakthrough premiership victory in 1992 and the follow-up in 1994.
Brennan retired following the 1995 season. At the time, his 179 games was a club record. He was honoured by being selected at full-back in the West Coast Team of the Decade in 1996 and in a back pocket alongside premiership teammate Ashley McIntosh in Team 20 in 2006.
Brennan works as a mortgage broker. In 2011 he was named as the club's number 1 ticket-holder. At the same time his son Jacob joined the playing squad as the first “true” father-son selection in West Coast history (though others such as McIntosh and Ben Cousins were selected based on their father’s WAFL careers).