 In October 2012, it was announced that Leicestershire had signed O'Brien in a three-year deal.His innings of 72 from 107 balls in the 2007 Cricket World Cup group match against Pakistan helped Ireland earn an upset victory and also earned him the man of the match award.O'Brien was one of seven Ireland players to be nominated for the 2009 Associate and Affiliate Player of the Year (there were fourteen nominees in all), although he did not make the 4-man short-list.