Williams, who last season appeared in eight games for the New York Giants, provides insurance as an interior lineman in a group that includes Sebastian Joseph-Day, Morgan Fox, Austin Johnson and Otito Ogbonnia.
Johnson and Ogbonnia both suffered season-ending injuries in Week 9 and Week 10, respectively, last season. General manager Tom Telesco said last month that their rehabilitation was "good so far." However, it remains unclear how much Johnson (left knee) and Ogbonnia (quad) will participate during mandatory minicamp and training camp.
Williams, 33, is anticipated to contribute as both continue to recover, then provide depth when the season arrives.
In New York last season, Williams was placed on injured reserve after suffering a biceps injury in Week 8. He recorded 15 tackles in seven starts.
In trend with several Chargers free agent signings over the past two years, coach Brandon Staley has direct experience with Williams, who spent the 2018 and 2019 seasons in Chicago, coinciding with Staley's time serving as the Bears' outside linebackers coach.
In 2019, Williams produced a career-best season with six sacks and 42 tackles in 16 games, including five starts.