 Williamson was a longtime member of the Lighthouse All-Stars (substituting for pianist Russ Freeman), performing with Bud Shank, Stan Levey, Bob Cooper, Conte Candoli and Howard Rumsey.In 1956, he became the piano player in the Bud Shank quartet.In 1968, he started working as a pianist for NBC, first on "The Andy Williams Show", then for Sonny and Cher.