Leighton was in his fourth spell at Pittodrie, having first joined as a player in 1977 and rejoined in the late 1990s as a player then coach before being let go under Mark McGhee’s management and brought back in soon after McGhee’s departure.
Dons boss Derek McInnes said: "I would like to thank Jim for his contribution as a member of my team since I arrived at the club."
It is not know who will replace Leighton. A club statement said: "Everyone connected with Aberdeen Football Club wishes Jim all the very best for the future."