Mendham came through the youth ranks at Carrow Road, and played 267 first-team games (211 in the league), and scored 29 goals for the Canaries. He was forced to retire because of injury in 1987. He was a member of the Norwich teams that won the Football League Cup in 1985, and the Second Division championship in 1986. Following his premature retirement, the club awarded Mendham a testimonial match against Real Sociedad, and he continued to work for the club for several years as 'Football in the Community Officer'.