Penn, 36, was released by the Oakland Raiders this off-season after five seasons with the franchise. The Raiders signed offensive tackle Trent Brown to a four-year contract and committed to second-year offensive lineman Kolton Miller, making Penn expendable.
Penn, who has primarily played left tackle in his career, switched to right tackle last season after the Raiders picked Miller in the first round of the 2018 NFL Draft out of UCLA. Penn played only four games, finishing the year on injured reserve due to a groin injury.
The three-time Pro Bowler has started 174 of the 178 games he has played in during his 12-season NFL career. He spent seven seasons with the Tampa Bay Buccaneers and was a two-time Pro Bowl choice in five seasons with the Raiders.
Along with sitting out training camp, Williams didn't participate in the Redskins' mandatory minicamp in June over issues with the franchise's medical staff, according to ESPN. He expressed his displeasure with how the Redskins handled the removal of a growth from his head this off-season.