Chelios has played in more games than any other American-born NHL player, and he joins the Thrashers after getting five goals and 17 assists in 46 games with Chicago of the AHL. The team recalled Chelios on Wednesday.
The Thrashers are looking for Chelios to provide a spark and help snap a three-game losing streak. Atlanta plays at Columbus on Thursday night.
Chelios has played 25 NHL seasons, winning three Stanley Cups and three Norris Trophies as the league's top defenseman.
"Chris has been an outstanding leader and mentor for our young players in Chicago and his level of play has made him deserving of this opportunity," said Thrashers general manager Don Waddell. "He's a tremendous competitor who strengthens our group of defensemen and instantly adds a veteran presence to our locker room."
Chelios is the second-oldest to play in the NHL. Only Gordie Howe, who played at 52, was older.
"I'll be satisfied to be the oldest American," Chelios said last year after ending his 10 years with the Detroit Red Wings.
Chelios was limited to 28 games with Detroit during the 2008-09 regular season because of a broken leg suffered during an exhibition game. He played in six games during the playoffs.
He has 948 points in his career with Detroit, the Chicago Blackhawks and Montreal. He has appeared in an NHL-record 266 Stanley Cup playoff games and is a three-time captain for the U.S. Olympic team.
