O' Cuinneagain first played for Ireland at A level and on 3 April 1998 played against England A in a 40–30 away defeat. Between 1998 and 2000 he made 19 full appearances and scored one try for the senior Ireland team. He made his senior international debut in a 37–13 defeat against South Africa on 13 June 1998. He played in all four games during the 1999 Five Nations Championship and then captained Ireland on both a tour of Australia and during the 1999 Rugby World Cup. He scored his one and only try for Ireland on 15 October 1999 in a World Cup game against Romania. He made his final appearance for Ireland in a 60–13 win against Italy at Lansdowne Road on 2 March 2000.