Farrell was born on 24 September 1991 in Wigan, Greater Manchester. He began playing rugby league in his hometown at the age of eight for Wigan St Patricks. When his father Andy signed for Saracens in 2005, his family moved to Harpenden, where Owen at the age of 13/14 was introduced to rugby union for the first time.
He held the record of youngest player ever to appear in English professional rugby union after playing for Saracens 11 days after his 17th birthday, in a 26–17 home defeat against Llanelli Scarlets in the EDF Energy Cup on 5 October 2008, until this record was broken in November 2009 by Leicester's George Ford.
In the 2010–11 season, Farrell signed for Bedford Blues on loan. However, he returned to Saracens and was pivotal in the 2010–11 Aviva Premiership Final kicking five penalties and converting James Short's try for a personal haul of 17 points in the 22–18 victory over reigning champions Leicester Tigers.
In the 2014-15 season, Farrell won the Man-of-the-match award in the Premiership Final, scoring a try and kicking a further 10 points. Saracens went on to win the final 28-16.
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