O'Leary scored his first try for Ireland in the 29–11 2010 Six Nations Championship opener against Italy. O'Leary was awarded Man of the Match for his outstanding performance during Ireland's 27–12 win over Wales at Croke Park on 13 March 2010. He broke his thumb against Leinster in October 2010 and was ruled out for 6–8 weeks. O'Leary recovered to fitness and featured against Italy and France during the 2011 Six Nations, but a troublesome back and a freak eye injury sustained during training ruled him out of the remainder of the tournament. Injury and the form of Conor Murray kept him out of the Munster team for the rest of the 2010/11 season, but O'Leary was selected in Ireland's training squad for the 2011 Rugby World Cup warm-ups in August. However, O'Leary did not make the final 30-man squad for the World Cup in New Zealand.