A right-back, Locke spent much of his career at Chelsea, making more than 300 league and cup appearances for the west London side between 1972 and 1983. He turned professional in July 1971, made his debut in a 3–1 win against Coventry City in the First Division on 30 September 1972, and scored his first goal for the club against the same opponents on 24 August 1974. He was chosen Chelsea Player of the Year in the 1973–74 season.
In 1983, after a spell on loan at the club, he moved to Crystal Palace on a permanent basis, making another 101 league and cup appearances in total, before spending the 1986 season in Sweden with Halmstads BK.
In 1987 Locke was brought to New Zealand by newly promoted national league club Napier City Rovers. He captained the team in 1988 and helped the club win the national league championship in 1989. Locke was left out of Napier's squad for the 1992 national league campaign.