O'Byrne made his Munster debut on 5 September 2014, starting against Edinburgh in the first game of the 2014–15 Pro12 season. He signed a one-year development contract with Munster in March 2015. On 3 September 2016, O'Byrne went off injured in Munster's 2016–17 Pro12 fixture against Scarlets. He was subsequently ruled out for 3 months with an elbow injury.