He won his first international cap for Ireland against Scotland on 19 February 2000 during the 2000 Six Nations Championship. O'Gara scored all of Ireland's points in their 18–9 win over Australia at Lansdowne Road in the Autumn Tests of 2002. He was a member of Ireland's 2003 Rugby World Cup squad, and played in all four Pool matches against Romania, Namibia, Argentina and Australia, and in the quarter-final loss to France. In total, O'Gara scored 30 points during his first Rugby World Cup.