Williams, who missed the entire 2020 season because of a torn labrum in his shoulder that required surgery, was released by the Raiders last month.
He signed a four-year, $44.4 million contract that included $22 million guaranteed with the Raiders as a free agent in 2019. All the guaranteed money has been paid out in his contract, and the Raiders saved $11.6 million against their cap by releasing him.
Williams, who turned 29 in February, had 42 catches for 651 yards and six touchdowns for the Raiders in 2019. But plantar fasciitis in both feet slowed him and he missed two games.
He spent the first four seasons of his career with the Chargers and had 155 receptions for 2,530 yards and 17 touchdowns in 55 games. His best season came in 2016, when he had 69 receptions for 1,059 yards and seven touchdowns.
The move to Detroit reunites Williams with Lions offensive coordinator Anthony Lynn, who was the Chargers’ head coach when Williams was on the roster in 2017 and ’18.