Born in Dublin, O'Leary signed for Shamrock Rovers in 1977 under Johnny Giles and made his debut in October[1] and went on to win the FAI Cup in 1978.
The tall centre-half made his Celtic debut in a 2–1 Scottish Cup victory at Hamilton Accies on 30 January 1985.
He then made enough appearances to claim a League Championship medal after Celtic pipped Hearts for the title on the final day of the 1985–86 season.
[2] Prior to retiring from football in 1988, O'Leary had set up an industrial cleaning business in Glasgow in partnership with Packie Bonner.
[3][4] Bonner's involvement only lasted a few years, but under O'Leary the business secured numerous contracts with offices, shops and hospitals.