Harper started his career at Ipswich Town, who were struggling in the Second Division in 1965–66. He made his first-team debut on 19 February, in a 3–0 defeat at Plymouth Argyle. He turned professional under manager Bill McGarry, and helped the "Blues" to rise to fifth in 1966–67, before finishing top of the division in 1967–68. They retained their First Division status in 1968–69, after Bobby Robson was appointed as manager. Ipswich hovered above the relegation places in 1969–70 and 1970–71, before rising to 13th in 1971–72. He scored his first senior goal on 9 October 1971, in a 1–1 draw with Nottingham Forest at Portman Road. He was sent off for the first-time in his career on 15 April 1972, during a 0–0 draw with Sheffield United. Three days later he scored the second goal of his career, his header helping to deny Manchester City the title as it proved to be the winning goal in a 2–1 victory on the penultimate day of the season. Town finished fourth in 1972–73 and 1973–74. However Harper picked up a knee injury in 1973 that would plague the rest of his career. The "Tractor Boys" fourth-place finishes entitled them to compete in the UEFA Cup. They posted a third-place finish in 1974–75, and were just two points behind champions Derby County. Harper was granted a testimonial match in 1975. Ipswich dropped to sixth in 1975–76, before rising again to third-place in 1976–77, five points behind champions Liverpool. Harper had two loan spells in 1976–77, playing three Third Division games for relegated Grimsby Town and 15 games under Ron Atkinson on loan at Fourth Division champions Cambridge United.
Port Vale
Harper joined Third Division club Port Vale as player-coach in July 1977, with manager Roy Sproson appointing him to replace Roy Chapman. He made his debut in a 1–1 draw at Wrexham on 27 August, but was to only make a further three appearances for the "Valiants" in 1977–78. He was made acting manager on 18 October 1977, and insisted that there was to be no smiling during training as it was a serious matter. His reign at Vale Park only lasted a month as new manager Bobby Smith brought in his own staff, including assistant Dennis Butler, and Harper's contract was cancelled by the club in January 1978.
Later career
After leaving Port Vale he was then appointed player-manager of Waterford. He led the "Blues" to the FAI Cup semi-finals and fifth in the League of Ireland. He signed with Sudbury Town in September 1978. He gave up playing three months later due to arthritis in his knee, though he stayed on at the club as manager. He then moved on to Chelmsford City, and led the club to an 18th-place finish in the Southern League in 1980–81.
Post-retirement
Harper became a builder after leaving the game. In May 2002, it was reported by the Ipswich Star that he had £7,000 worth of tools stolen from his van in Ipswich. He continued to follow Ipswich Town until his death from illness on 29 March 2018; he left behind wife Carol, and three children, Chris, Jamie and Zoe. An inquest revealed that he died from an asbestos-related disease, having been exposed to asbestos whilst working as an apprentice joiner and carpenter before he took up his football career.
