[2] Horn played for Heart of Midlothian, Cowdenbeath, Forfar Athletic and Berwick Rangers in the Scottish Football League.
After a stint as manager of Vale of Leithen, Horn assisted Colin Cameron at Berwick.
[3] He was appointed manager of junior club Bonnyrigg Rose Athletic in June 2015.
[4] Horn led Bonnyrigg to the East Super League championship in 2015–16.
[3][6][7] He resigned from this position in October 2018, with the club in second-bottom place in the 2018–19 Scottish League Two table.