Farrell was a member of a Christian punk/ska band called Tasty Snax. While he was at the college, he shared the room with his friend Brad Delson, and they practiced together.
He had to go on tour with the Tasty Snax so he could not play with Delson and his band. Then, Farrell left his band to play bass with Brad Delson in the band Xero in 1996 but then left in 1998. He then rejoined Xero now called Linkin Park in November 2000 and has been playing with them ever since.