Williams said in a team-issued statement Tuesday that he met with Bucs general manager Mark Dominik about his future and "after a lot of thought" decided it was time to part ways.
A first-round draft pick in 1978, Williams led Tampa Bay to the playoffs three times in five seasons. After a brief stint in the USFL, he played with the Redskins from 1986 to 1989.
Williams rejoined the Bucs as a personnel assistant in 2004.
"I have tremendous respect for Doug's talents and am very appreciative of his many contributions to this franchise over the years," Dominik said in the statement. "At the end of last season, Doug and I began a conversation regarding his career. Doug concluded that now is the time for him to make the smoothest transition. Like Mike Alstott and Lee Roy Selmon, Doug will stay involved as a representative of the team in the community."
The Associated Press contributed to this report.