Farrell grew up in Fivemiletown, a village in south Tyrone, Northern Ireland. His initial sporting passion was soccer and he played centre-half for a local team, before he started playing rugby at the age of 11 for Clogher Valley RFC in County Tyrone.
On 24 January 2017, it was announced that Farrell would be joining Irish province Munster on a two-year contract, beginning at the conclusion of the 2016–17 season. Farrell made his competitive debut for Munster on 1 September 2017, starting the provinces opening 2017–18 Pro14 fixture against Benetton in Irish Independent Park, Cork. Farrell scored his first try for Munster in their fixture against South African side Cheetahs on 9 September 2017, helping the province to a 51–18 win in Thomond Park. He was ruled out for 6–8 weeks following a knee injury sustained whilst playing for Ireland. He returned from the injury on 6 January 2018, starting in Munster's 39–13 win against Connacht. A knee injury Farrell suffered while with the Ireland squad during the 2018 Six Nations required surgery, and subsequently ruled him out of the remainder of the 2017–18 season. He signed a three-year contract extension with Munster in October 2018, a deal that will see Farrell remain with the province until at least June 2022. Farrell returned from the aforementioned knee injury on 25 November 2018, featuring off the bench in Munster's 2018–19 Pro14 round 9 fixture against Italian side Zebre. He scored two tries and earned the Man-of-the-Match in Munster's 44–14 win against Edinburgh on 30 November 2018.
Ireland
Farrell earned his first senior international call-up in October 2017, being named in the Ireland squad for the 2017 Autumn Internationals. He made his first appearance for Ireland on 18 November 2017, starting against Fiji. Farrell also started in Ireland's win against Argentina, though he went off injured during the second-half. Farrell made his Six Nations debut on 24 February 2018, starting against Wales and earning the Man-of-the-Match award in Ireland's 37–27 win. However, a knee injury sustained during training ruled Farrell out of the remainder of the tournament. He was selected in the 31-man Ireland squad for the 2019 Rugby World Cup, having featured in the warm-up matches against Italy, and Wales.
