O'Brien hit the first century for Ireland in Tests in their debut match v Pakistan in 2018.
O’Brien played a memorable knock in the 2011 World Cup in Bengaluru, hitting a 50-ball century, the fastest in World Cup history, to help the Ireland side beat England by chasing down a 328-run target.
He also scored the first Test century for Ireland in their debut match against Pakistan in 2018 and remains the only Irish player with a century in all three forms of international cricket.
O'Brien announced his retirement in a long post that he shared on Twitter. In his post, O’Brien said that he had hoped to retire after playing in the upcoming T20 World Cup, but a lack of opportunities has led him to take the decision to hang his boots.
"Today I announce my retirement from international cricket after 16 years and 389 caps for my country. I had hoped to finish my career at the T20 World Cup in Australia but having not been picked for the Irish squad since last year's World Cup, I feel that the selectors and management are looking elsewhere. I have enjoyed every minute playing for Ireland, made many friends on the pitch and I have so many happy memories to remember from my time playing for the National side," he wrote.
"I have enjoyed every minute playing for Ireland, made many friends on the pitch and I have so many happy memories to remember from my time playing for the National side. It's now onto the next stage of my life and my career for me, the time is right. I want to continue to grow my own Coaching Academy here in Ireland and I have some exciting opportunities coming up in the near future. I also want to continue to gain coaching experience overseas and hopefully will have more opportunities with some international and professional sides in the near future," O'Brien added further.