Barber finishes his NFL career with 4,780 yards with 53 touchdowns.
Barber's decision comes one day after Michael Bush signed a four-year, $14 million contract to be part of a Chicago backfield that includes disgruntled Pro Bowl running back Matt Forte.
Barber was selected by the Dallas Cowboys out of the University of Minnesota in the fourth round of the 2005 draft. His most productive seasons came as a Cowboy -- he had 14 touchdowns in 2006 and then rushed for a career-high 975 yards in 2007 en route to earning a trip to the Pro Bowl.
Barber had six touchdowns and 422 rushing yards for the Bears in 2011, but he'll be remembered for two gaffes in a costly loss at Denver when he ran out of bounds as the Bears were trying to kill the clock, and then fumbled in overtime.
Barber, who had little to say to reporters during his only year in Chicago, told the Bears' official website: "I want to thank everyone who gave me the opportunity to play, and I'm very thankful to have had the chance to suit up for two of the NFL's most storied organizations."
"I want to thank everyone who helped me become a better player," Barber said. "I owe a lot to a lot of coaches, and am also very grateful to the owners and organizations I played for. Last but not least, I want to thank the fans for the support and inspiration they gave me."
The Associated Press contributed to this report.