 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.On 23 March 2018, in Ireland's match against Afghanistan in the 2018 Cricket World Cup Qualifier, O'Brien played in his 100th ODI match.In May 2018, he was named in a fourteen-man squad for Ireland's first ever Test match, which was played against Pakistan later the same month.