Farr was drafted by the Detroit Lions in the first round, seventh overall pick, of the 1967 NFL Draft and played seven years as a running back for the Lions. He led the Lions in both rushing and receiving in 1967, totaling 1,177 yards from scrimmage as a rookie, and was selected as the NFL Rookie of the Year. He was twice selected to play in the Pro Bowl, in 1967 and 1970. In a career shortened by injury, Farr gained a total of 4,446 yards from scrimmage and scored 36 touchdowns during his seven years in the NFL.