In 2007, he was selected to officiate at the FIFA Under-20 World Cup in Canada during June and July of that year. He took charge of the Group F game between Nigeria and Costa Rica at the Royal Athletic Park in Victoria, British Columbia, on 1 July. He was then assigned the Group B match between Uruguay and Jordan at the Swangard Stadium in Burnaby, on 4 July. At the English Premiership tie between Aston Villa and Sunderland F.C. as a guest of top English referee Steve Bennett, O’Leary was summoned from the stands to assume Bennett's role on the touchline as 4th official for the second half of the match.