O'Mahony was born in Cork, Ireland, where he attended Presentation Brothers College. O'Mahony went on to join the Munster Academy in 2008 and captained Ireland U20 at the 2009 Six Nations Under-20s Championship and 2009 IRB Junior World Championship.
The ideal modern backrow, O’Mahony can play comfortably at 6,7 or 8, possessing the physical and tactical nous to play in any of the back row positions. At the tender age of 23, he captained Munster for the duration of the 2011 World Cup, when the Senior Munster players were away with Ireland.
O’Mahony was named Man of the Match in his maiden Heineken Cup game against Northampton in November 2011. Due to his impressive form during the 2011-2012 season, he was named IRUPA’s young player of the year.
This form for Munster led to an Ireland call up and he made his debut against Italy in the 2012 Six Nations Championship. He scored his only international try in a 40-9 win over Samoa on 9 November, 2013. He played a vital part in Ireland's successful 2014 and 2015 Six Nations campaigns. The Munster captain excelled in the 2015 season for his home province, leading to his inclusion in the Ireland squad for the 2015 World Cup in England.
He signed a new three-year contract with Munster and the IRFU in February 2015, which will see him remain with the province until at least June 2018.
The Munster stalwart continued his fine form for Munster into the green of Ireland for the 2017 6 Nations tournament, with a stand out performance against champions England.
Before the British & Irish Lions squad was announced on the 19th April, O'Mahony admitted he was “not expecting anything” in terms of a call-up.
In April 2017, O'Mahony was named in the 41 man British & Irish Lions squad on the tour to NZ, his 1st tour with the Lions. At the time of selection, O'Mahony has 40 Irish caps.
On 17th June, O'Mahony captained the Lions against the Māori All Blacks in Rotorua International Stadium. In doing so, he became the first Munster player since Paul O'Connell in 2013 to captain a Lions team.
On 21st June 2017, O'Mahony was named the captain of the British & Irish Lions for the first Test in Eden Park, becoming the 11th Irish player to captain the side.
O'Mahony featured in all of Ireland's Six Nations matches taking his test cap tally to 50 following the June Tests against Australia.
He heads into the 2018/19 with 107 caps for Munster, having scored 60 points.
As of the 2018/2019 Champions Cup, O'Mahony has had 42 European Cup appearances scoring 5 tries and 25 points.
In April 2019, he was named Munster's Player of the Year for 2019.
O'Mahony has been named for the 2020 Six Nations Ireland squad and has 64 caps.
|2010 - present|
|2012 - present|
|Presentation Brothers College
|British & Irish Lions
|2017 - present|