Barker was recruited from the Cheltenham Football Club in 1975. He made his debut wearing number 25 against Hawthorn in round 2 on 12 April 1975. He changed to his iconic number 1 in 1977. He was selected to represent Victoria at interstate level on seven times. Barker won St Kilda's best and fairest award in 1976 and 1981. Barker played during an era of little club success, which included St Kilda being wooden spooners in 1977, 1979, 1983–86 and 1988. Barker was captain of the St Kilda Football Club from 1983 to 1986. He was regularly featured in the VFL highlight reels with his high-marking and determined approach to the ball. Barker's 230 games did not include a final, a VFL/AFL record, and he is one of only five players in the AFL/VFL to play 200 games or more without appearing in a final. As he got older he would regularly miss games through chronic injury until he retired after the 1989 season. Many football experts noted that Barker could have easily fitted into the powerhouse teams of the competition and there were plays for his services but his loyalty never wavered and he stuck with the club throughout his entire career.
Coaching
After retiring from the Saints in 1989, Barker embarked on a coaching career with Victorian Football Association club Sandringham. He coached the Zebras to premierships in 1992 and 1994 before leaving after his second premiership to return to the Saints as an assistant coach to Stan Alves coaching the reserves team and mentoring young players.
Barker had to put his coaching career on hold midway through the 1995 season for health reasons. He died on 26 April 1996. Barker was 39 when he died when his liver failed after a prolonged battle with colon cancer.
Legacy
His contribution to St Kilda, particularly in the 1980s when the club had severe financial difficulties, was significant. St Kilda's best and fairest award, instituted in 1914, is named the Trevor Barker Award as a mark of respect to his contribution to the St Kilda Football Club. Barker was named in the club's Team of the Century 1900–1999. His name was also inducted to the St Kilda Football Club Hall of Fame in 2003. The home of the Sandringham Football Club was also named Trevor Barker Beach Oval, in his honour. His name was officially elevated to Legend Status in the St Kilda Football Club Hall of Fame on 4 May 2013 at an official club function. On 4 June 2019 he was inducted into the Australian Football Hall of Fame.
