Mansfield moved to the Steelers in 1964, played left defensive tackle for his 1st two years with the Steelers and was their starting center beginning in the 1966 season through the 1976 season. He was a member of the Steelers' Super Bowl-winning teams in 1974 and 1975. In his last season as a Steeler, he kicked the extra point on the Steelers' final touchdown in a playoff game after Roy Gerela pulled a groin muscle.
Mansfield went on to a successful career as an insurance broker. He died from a heart attack in November 1996 while hiking in the Grand Canyon.