 O'Brien set a World Twenty20 record with his 4 dismissals against Sri Lanka in the Super 8 stage of the 2009 ICC World Twenty20.O'Brien was selected in Ireland's 15-man squad for the 2011 World Cup to be hosted by Bangladesh, India, and Sri Lanka between February and April.During the tournament he became the third player to score 1,000 ODI runs for Ireland after William Porterfield and his brother Kevin.