Williamson played college football for Chicago's Northwestern University during the late 1950s. This was followed by a seven-year professional career in the NFL, beginning in 1960 when he was signed on with the Pittsburgh Steelers. The following year, he joined the Oakland Raiders, with whom he played four seasons. He then played three seasons with the Kansas City Chiefs. It was during this time he became known as "The Hammer", and was a starter in the very first Super Bowl.