O'Mahony plays as a flanker. He was an integral part of the team when the internationals were away for the November Tests , putting in a big performance in Munster's historic 15—6 victory against Australia , a game which was also O'Mahony's first start for Munster.
O'Mahony captained Munster in their opening Pro12 match against Dragons in September , [ 10 ] and continued to captain Munster whilst their international contingent were away at the Rugby World Cup. O'Mahony started for Munster in their opening fixture of the —13 Heineken Cup on 13 October , a 22—17 defeat at the hands of Racing O'Mahony was named as the new Munster captain on 30 July , replacing former All Black Doug Howlett , who retired at the end of the —13 season.
O'Mahony started the 20—7 away win against Gloucester on 11 January , scoring a try in a win that secured quarter-final qualification. O'Mahony returned from injury on 4 October , coming on as a replacement against Leinster. O'Mahony started against Saracens on 17 January O'Mahony made his comeback from the knee injury he suffered with Ireland during the Rugby World Cup on 1 October , coming on as a replacement for Billy Holland in the —17 Pro12 fixture against Zebre.
O'Mahony won his th cap for Munster on 26 December , doing so when he started against Leinster in a —18 Pro14 fixture. O'Mahony was sent off in Munster's opening —21 Pro14 fixture against Scarlets on 3 October after receiving two yellow cards.
Despite this, Munster won the game 30—27, and a Pro14 judicial officer subsequently ruled that the two yellow cards were sufficient and no ban was necessary. Having missed the first leg of Munster's —22 Champions Cup round of 16 fixture away to English club Exeter Chiefs due to injury, which the hosts won 13—8, O'Mahony returned for the second leg one week later on 16 April to lead from the front and earn the player of the match award in the province's 26—10 home win, which secured a 34—23 aggregate win and a record-equallinging 19th Champions Cup quarter-final for Munster.
