The Wales defender, 27, was released by Sunderland after making 28 appearances for the League One club last season.

Matthews started his career at Cardiff, going on to spend four years at Celtic before joining the Black Cats in 2015 - when they were in the Premier League.

"It's been a tough summer for me personally, not knowing what was going to happen," he said.

Charlton head of recruitment Steve Gallen added: "He's completely proved his fitness and that he's got a good attitude so he fully deserves the offer of a contract and balances out the squad."

Lee Bowyer's Addicks are second in the Championship after winning four and drawing two of their first six games.