Horton played at wing-half, though was forced to find employment as a builder after being released from Walsall's youth-team in 1966. He joined Hednesford Town in the West Midlands (Regional) League, winning the Staffordshire Senior Cup in his final appearance for the club in 1970. He turned professional in signing with Port Vale of the English Football League in July 1970. He established himself in the first-team, making 258 appearances, before being sold on to Brighton & Hove Albion for £30,000 in March 1976. Installed as club captain, he helped the club to win promotions to the First Division from the Third Division in 1976–77 and 1978–79, being named on the PFA Team of the Year on both occasions. He also won the club's Player of the Year in 1977. Having played 251 games for the club, he was transferred to Luton Town in August 1981. He captained the team to the Second Division title in 1981–82 and helped the club to remain in the First Division, playing 132 games in league and cup competitions.