Williams had been listed as questionable with a knee injury after missing practice this week. Chargers coach Brandon Staley said Williams' knee had some swelling after last Sunday's 47-42 win over the visiting Cleveland Browns.
"We just tried to be careful with him this week at the beginning of the week, make sure that he's feeling his best for Sunday," Staley said.
Williams has 31 catches for 471 yards this season. He leads the league in touchdown receptions with six.
Both the Chargers and Ravens head into Sunday's game at 4-1 and leading their respective divisions.
Information from The Associated Press was used in this story.