Williamson was a wide receiver under legendary Alabama coach Bear Bryant for the 1961 and 1962 seasons. He caught Joe Namath's first touchdown pass at Alabama. Williamson would move over to the coaching staff from 1963–1967, helping the Tide win National Championships for the 1964 and 1965 seasons.
After a two year coaching stay at the University of Arkansas, Williamson returned to Alabama for 1970-1971 before leaving for Arkansas again (from 1972 to 1974). Williamson then left for Memphis State University, this time becoming head coach (1975–1980). Williamson's teams finished 7-4 (1975, 1976), 6-5 (1977), 4-7 (1978), 5-6 (1979), and 2-9 (1980). Williamson was honored with the Southern Independent Conference Coach of the Year award twice.
Williamson moved to the pro ranks after being released from the Memphis State job in 1980, moving on to the Kansas City Chiefs under new coach John Mackovic. Williamson rejoined the football ranks in 1987 with the Tampa Bay Buccaneers, working under fellow former Alabama coach Ray Perkins as offensive coordinator. When Perkins was fired late in the 1990 season, Williamson was named interim head coach, leading the team to a 1-2 record. Named head coach in 1991, Williamson went 3-13 before being fired at the end of the season.
In 2000, Williamson was named assistant head coach under George Seifert; he was later named offensive coordinator as well, after Bill Musgrave resigned four games into the season. After the 2001 season, Williamson returned to coachng the receivers under new head coach, John Fox. Williamson developed outstanding wide receivers during his professional career including Muhsin Muhammad and Steve Smith with the Panthers. Williamson announced his retirement on January 18, 2010, after 15 seasons with the Panthers.