Farrell grew up in Castlemaine, Victoria supporting the Geelong Cats. He played junior football with Winters Flat in their under-10s team through to their under-15s team. Farrell then played for Castlemaine Football Club and the Bendigo Pioneers' under-15s, 16s and 18s teams.[3] He represented Vic Country in the 2017 AFL Under 18 Championships, averaging 14 possessions and three marks per game.[4] At the 2017 AFL Draft Combine, Farrell recorded the equal-best time of 8.10 seconds in the agility test and the second-best 20 m (66 ft) sprint with a time of 2.90 seconds.[5] He was drafted by Port Adelaide with their second selection (no. 51 overall) in the 2017 national draft.[6] Farrell inherited number 24 from Jarman Impey.[7]
Farrell was named in Port Adelaide's 2018 AFLX squad.[8] Before his AFL debut, he played 13 matches in the South Australian National Football League, kicking 20 goals.[4] Farrell was named as an emergency for the senior side in the two weeks before his first match.[9] Ahead of his debut, Port Adelaide development coach Aaron Greaves described him as a "lovely left foot" and a "classy finisher".[10]
Farrell's parents are Sue and Stephen. He has one brother, Brodie.[3]