The Panthers sent a sixth-round pick in 2016 to the Bears on Monday for Allen, who has more sacks (134) than any active NFL player.
Allen gives the Panthers a proven pass rusher in the absence of Charles Johnson, who'll miss at least one game with a strained hamstring.
Panthers general manager Dave Gettleman says in a release ''when you have a chance to add a quality player to your roster you must take advantage of the opportunity.''
A fourth-round draft choice in 2004, Allen has been named to five Pro Bowls and is a four-time All Pro.
Allen is expected to play Sunday at Tampa Bay.