The Frenchman had been linked with a switch to Tottenham before the Black Cats bought him.
Ba scored on his debut in an FA Cup win over Carlisle in January 2014, having signed from La Havre in 2013, but found game time hard to come by at the Black Cats.
The youngster ended up heading out on loan to Bastia back in France at the start of last season, having made just three appearances for Sunderland, but unfortunately suffered a broken leg after arriving in Corsica.
The 22-year-old midfielder was happy to have made the move to the Valley this summer as he sought to rebuild his career, recognising that things didn't go his way at the Stadium of Light.
“It’s very nice to be a Charlton player," he told the Charlton website. “I’m very happy to be here. It was a little bit difficult at Sunderland.
“I was young and didn’t have a lot of time on the pitch but now I am older and ready to fight at Charlton.”
Can Charlton salvage Ba's career?
The Paris born player was a highly sought after player as a youngster, featuring for the French Under-20s and being coveted by Tottenham according to L'Equipe.
Ba made seven appearances in the French top flight this season before his injury, and is plenty young enough to be a superb addition to a Championship side.
Pre-season and the Addicks' opening games will be an indication as to just how good a signing Ba ends up being for Guy Luzon, but supporters should be encouraged that the club have managed to seal the signing of a player who still has a lot of potential to try and reach.