The 27-year-old, who can play in defence or midfield, is set to put pen to paper on a two-and-a-half year contract at The Den.
Williams is the Dons' current player of the year and has made 33 appearances for Karl Robinson's side this term, scoring 10 goals.
He will become new Lions manager Ian Holloway's third signing of the transfer window, joining Ryan Fredericks and DJ Campbell, and will be in contention to make his debut against Sheffield Wednesday on Tuesday night.
- Sports & Recreation
- Karl Robinson
- Ryan Fredericks