Sunderland signed Charlton's Republic of Ireland midfielder Andy Reid just hours before the close of the January transfer window in a deal which could cost them four million pounds.
The north-east club, who are three points above the Premier League drop zone, have signed the 25-year-old on a three-and-a-half-year deal.
Sunderland manager and former Republic midfielder Roy Keane told the club's official website: "Andy brings added quality to our side in an area that I felt needed to be strengthened."
The clubs had announced earlier Thursday that defender Greg Halford would be making the opposite journey to the second-tier Championship club's south London home at The Valley.
Halford, 23, has made eight league appearances for Sunderland this season and Charlton manager Alan Pardew said: "Part of doing business is to make sure you try to do something that's useful for your club.
"I lost Jermain Defoe in a similar situation when I was at West Ham United, and brought in Bobby Zamora," he said. "Hopefully, we can have similar success with Greg. He's coming here on loan and I think he's got a lot to prove.
"It didn't work out for him at Reading, it didn't work out for him at Sunderland, so I think he needs to be a success here, but I think he will be a massive asset for us."