The veteran defenceman was dealt to the Boston Bruins by St. Louis for a seventh round pick in the 2014 draft.
Redden was signed by the Blues after being bought out by the New York Rangers just after the lockout. He signed a six-year, $39 million free-agent deal with the Rangers in 2008 to leave Ottawa, where he was an all-star.
But his play slipped, and his contract was too high a commitment for other teams to take on. As a result, he was sento the minors and spent two seasons in the American Hockey League.
The Lloydminster, Sask., native had two goals and three assists in 23 games with St. Louis, but was made expendable when the Blues in recent days traded for blue-liners Jay Bouwmeester and Jordan Leopold.
He was signed to a one-year deal worth $800,000 US prorated.
In Boston, the 35-year-old will be reunited on the ice with Zdeno Chara and Chris Kelly (currently injured), both former Senators. Bruins general manager Peter Chiarelli, meanwhile, was with Ottawa's front office when Redden had his best NHL years.
In 1,017 career NHL games, Redden has 108 goals and 347assists, with 665 penalty minutes.
The Bruins earlier got together with the Blackhawks for a minor deal.
Boston has sent forward Maxime Sauve to Chicago in exchange for forward Rob Flick.
Sauve will be assigned to the Rockford IceHogs of the American Hockey League.
He recorded 23 points (10 goals, 13 assists) in 52 games this season with the Providence Bruins of the AHL.
The 22-year-old Flick is a year younger than Sauve.
Flick has five points (3-2) in 51 games with Rockford this season.