[7][8] He rapidly developed a reputation as a prodigious goalscorer and following a record-breaking haul of 33 goals in 34 league games in the 1971–72 season was the subject of much interest from English scouts.
[9] Harper was never a favourite with the Hibs fans,[7] and his arrival signalled the beginning of the decline of the team's fortunes through the late 1970s and 1980s.
Harper returned to Aberdeen under Ally MacLeod for the start of the 1976–77 season in a £50,000 deal and inspired instant success, the Dons defeating Celtic 2–1 (after extra time) to win the League Cup in November.
By the 1979–80 season he was considered a veteran and no longer a regular in the Dons first team but his seven goals helped Alex Ferguson become the second Scottish League-winning Aberdeen manager after Dave Halliday in 1954–55.
[13] He next played for Scotland in October 1972, scoring in a 4–1 win against Denmark,[7] and also took part in the following fixture but then fell out of the international reckoning, only earning a recall in 1975.
He helped the Blue Toon to a second place league finish but his reported wages were beyond the club's means and he was replaced for the 1982–83 season by former Pittodrie teammate Dave Smith.
[7] Harper was appointed honorary Club President of Aberdeenshire Amateur League side Halliburton AFC in 2009.
In the early 21st century he often worked on home match days for Aberdeen in as the host of the 'Legends' Hospitality Lounge of the Richard Donald stand at Pittodrie Stadium.