In a tour match against Australia during the 2009 Ashes in July 2009, O'Brien made scores of 30 and 58 in a match Northamptonshire lost. During his half century, he scored seven boundaries off the struggling Mitchell Johnson. O'Brien missed most of the 2010 season after undergoing finger surgery in July; in his absence, David Murphy was Northamptonshire's first-choice wicket-keeper. In 2012, O'Brien signed a contract worth $80,000 with Khulna Royal Bengals represent them in the newly formed Bangladesh Premier League, a domestic t20 competition. In five matches he scored 54 runs. At the end of the 2012 English County season, O'Brien left Northamptonshire after six seasons. 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. O'Brien was selected in Ireland's 15-man squad for the 2011 World Cup. 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. He passed this landmark in Ireland's five-wicket defeat to India. In the same match, O'Brien and Porterfield established a new records for Ireland's third wicket in ODI, putting on 113 runs together. Ireland were due to play two ODIs against Pakistan in May, however O'Brien suffered an injury to his hand and was forced to miss the fixtures. On 16 February 2015, he smashed unbeaten 79 runs off 60 balls with 11 fours, guided Ireland to the victory against another Test match playing nations, the West Indies. This was Ireland's third consecutive victory over test playing nations in three consecutive world cups. O'Brien's score was helped to beat mighty West Indian pace attack and finally Irish won their first match of 2015 ICC Cricket World Cup.