 In September 2019, he was named in Ireland's squad for the 2019 ICC T20 World Cup Qualifier tournament in the United Arab Emirates.Ahead of the tournament, the International Cricket Council (ICC) named him as the key player in Ireland's squad.Later the same month, during the 2019–20 Oman Pentangular Series, O'Brien became the first batsman for Ireland to score a century in a T20I match, when he made 124 against Hong Kong.