Williams' rookie contract with the Packers expired following the 2020 season. He rushed 119 times for 505 yards and two scores last year, adding 31 catches for 236 yards and one more touchdown.
The former BYU star's days in Green Bay appeared numbered after starting running back Aaron Jones reached an agreement on a four-year, $48 million contract to stay in town, per ESPN's Adam Schefter.
Backup AJ Dillon, who Green Bay drafted in the second round last year, is under team control for three more seasons, so it made sense for Williams to seek other opportunities.
Williams joins a crowded Detroit backfield that features D'Andre Swift and Kerryon Johnson. Adrian Peterson, who led Lions running backs in touches last year, has entered free agency.
Swift was a close second in touches, gaining 878 total yards and scoring 10 touchdowns on 160 touches. He was the most efficient running back on the roster and figures to be the team's No. 1 back.
Williams figures to be the No. 2 back in this offense. Both Benjamin Raven of MLive and Chris Burke of The Athletic said the Swift-Williams combo would be a nice two-man combination. Johnson could still see some work and should be the next man up in case Swift or Williams is unable to go in a given week.
Williams is the newest addition to a Lions offense that will look different from last year's unit. The team's leading passer (Matthew Stafford) will be a Los Angeles Ram, its leading rusher (Peterson) is a free agent who will not return, and its top two receivers (Marvin Jones Jr. and Kenny Golladay) aren't coming back.
Jones has agreed to terms with the Jacksonville Jaguars, per Ian Rapoport of NFL Network. Golladay is a free agent who should break the bank elsewhere and has garnered interest from the Miami Dolphins, according to ESPN's Cameron Wolfe.
Williams will play a key role in the Lions' new regime under general manager Brad Holmes and head coach Dan Campbell. The team is looking to bounce back from a 5-11 season that landed it in the NFC North basement.