The 30-year-old right-hander, who had been the Marlins closer for most of the past two seasons, was dealt to the Cubs for pitching prospect Jose Ceda.
"It's one of those teams, I've always said I've wanted to play there and play for the Cubs," Gregg said. "I can't say enough about the organization and the atmosphere there."
Since the World Series ended, the Marlins have now made three trades in which they moved players eligible for arbitration for younger talent. In all three deals, Florida received pitching in return.
Ceda, 21, is a 6-foot-4, 275-pounder who is currently pitching in the Dominican Republic Winter League for Leones.
"Jose is a big, strong kind with a real live arm," Marlins president of baseball operations Larry Beinfest said. "We think he can help us in the back end of our bullpen in the very near future, if not right away. We also want to thank Kevin for his two seasons with us. He did a great job for us and we wish him the best."
Entering his third season of arbitration, Gregg -- who made $2.5 million in '08 -- has been on the trading block since the season ended. The right-hander, initially acquired by the Marlins from the Angels after the 2006 season, is battling back from a left patella tendon injury.
Trading Gregg came after Florida sent lefty Scott Olsen and left fielder Josh Willingham to the Nationals for infielder Emilio Bonifacio and two Minor Leaguers on Monday, which was officially completed on Tuesday morning. On Oct. 30, first baseman Mike Jacobs was dealt to the Royals for reliever Leo Nunez.
For several weeks in the second half, Gregg was hindered by a sore left knee, eventually being replaced as the closer by hard-throwing Matt Lindstrom.
Gregg underwent surgery a few weeks ago to repair left patella tendinitis. He is expected to be ready by Spring Training.
August was an especially tough month for Gregg, who was sidelined after he was unable to convert a save against the Mets on Aug. 29.
Although he didn't go on the disabled list, Gregg rested his knee and he next pitched on Sept. 9. In nine appearances in September, the right-hander didn't allow a run in seven innings.
Unless the Marlins seek a closer elsewhere, the team is prepared to go into Spring Training with Lindstrom handling the role. Lindstrom converted all five of his save chances in September.
In two seasons with the Marlins, Gregg posted 61 saves in 74 chances. In 2007, he converted 32 of 36 chances and racked up 84 innings in 74 games.
At Double-A in '08, Ceda was 2-1 with a 2.08 ERA in 22 relief appearances, and he also made 12 starts and three relief appearances at Class A Daytona.
In 84 2/3 innings this past season, Ceda struck out 95 and walked 42.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.