Marshall fills an area of need for the Chargers before the draft in May. With the addition of Marshall, the Chargers have six corners on the roster.
Marshall, 29, solidified the cornerback position after Derek Cox lost his starting job with five games left in the regular season.
A second-round selection by Carolina in the 2006 draft, Marshall signed with the Chargers in August after being released by Miami at the end of training camp. He started five regular-season games and both of San Diego's playoff games.
He played 603 defensive snaps in the regular season and finished fourth on the team in tackles with 71. He also had six pass defections and a forced fumble.