In November 1956, O'Farrell left for Preston North End in a straight swap deal involving Eddie Lewis. Replacing Ray Evans in the team, he scored on his home debut, a 20-yard strike against Manchester City. Playing alongside Tom Finney, he played 17 league matches before his first loss with the club. He would then miss over a month of football after treatment for a nosebleed which caused him to lose around four pints of blood (he experienced a recurrence of the problem in the following season). His first season with Preston brought a third-place finish and he was still with the Lancashire club when they finished runners-up to Wolverhampton Wanderers in Division One at the end of the 1957–58 season. In the same season O'Farrell's former teammates at West Ham finished as Second Division champions, securing their promotion to the First Division, which he had strived to help achieve. In all, O'Farrell made 129 appearances for Preston, scoring four goals.