Williams was born in Okolona, Mississippi and began playing the piano after being inspired by his older brother Earl, who was a multi-instrumentalist. Williams's first band was called The Jays, after they disbanded he met the other founding members of the Commodores in 1967. They were freshmen at Tuskegee Institute, Alabama and Williams was recruited into the newly formed band. In 1969 he traveled with the band to New York City, where they recorded a single called "Keep on Dancing" on Atlantic Records.
Williams also wrote the Commodores first hitrecord the instrumental track, "Machine Gun". Other Commodores songs penned by him are; "The Bump", "Rapid Fire", "I'm Ready", "Better Never Than Forever", "Mary Mary", "Quick Draw", "Patch It Up", "X-Rated Movie", "Wonderland", "Old-Fashion Love", "Only You" (a track Williams also produced, taken from the Commodores first LP without Lionel Richie, Commodores 13), "You Don't Know That I Know", "Let's Get Started" and "Brick House".
He left the Commodores in 1989, allegedly after refusing to perform with them in South Africa.
Milan Williams died of cancer at a hospital in Houston on July 9, 2006 at age fifty-eight. His interment was at Zion Spring Cemetery in his hometown of Okolona, Mississippi.