Farrell was the first round draft pick of the Tampa Bay Buccaneers in the 1982 NFL Draft; Buccaneers management had actually intended to select defensive end Booker Reese, and Farrell's name was turned in due to a communication error in the draft room. The team then traded the next year's first round pick in order to get Reese as well. Ironically, Farrell played at a high level for the Buccaneers, while Reese ultimately came to be considered one of the most disappointing draft picks in team history.
Tampa Bay's team performance declined during Farrell's years with the team. After his first contract expired in 1985, he signed a one-year contract for the 1986 season based on the team's assurances that things would improve, but the team had another bad year and Farrell made news by publicly telling a group of Bucs fans, "I know what I want this Christmas . . . I want to get the hell out of Tampa Bay."New England acquired him in return for three draft picks, and he was the Patriots' starting guard for three seasons before shoulder surgery kept him on the injured reserve list for most of the 1990 season. Near the end of that season, the Patriots tried to reactivate him without using a protective designation for him; under the rules then applicable, this had the effect of putting him on waivers, and he was claimed by the Denver Broncos. He finished that year and played another in Denver, then one more for Seattle before concluding his NFL career.
After football, Farrell became a financial advisor with several investment companies including Merrill Lynch, and he is the chairperson of the Gay Culverhouse Player Outreach Program to assist former NFL players facing disability issues after their careers.