O'Leary's international debut with the Republic of Ireland came as a teenager in a 1–1 draw with England in 1976. Following the appointment of Jack Charlton, O'Leary was frozen out of the international setup for 2 years. After being left out of a squad for a mini tournament in Iceland in May 1986, O'Leary booked a family holiday, which he decided not to cancel when he was eventually asked up to the squad following several withdrawals. O'Leary did not feature until November 1988, thus missing out on Euro 88.