Sitton, 31, was due to make $8 million for the 2018 season, NFL Media reported Tuesday. He will become a free agent on March 14.
A four-time Pro Bowl selection, Sitton confirmed his release to the Chicago Tribune.
"I am planning on playing and hitting free agency and continuing to play at a high level," Sitton told the newspaper. "I believe I have prime years left."
Sitton said he had a "great conversation" with Bears general manager Ryan Pace and expressed appreciation that the team released him so he had plenty of time to draw attention on the free-agent market.
Injuries hampered Sitton during his two-year tenure with Chicago, as he missed seven games in that span after appearing in all 16 games over the previous four years with Green Bay.
A fourth-round draft pick out of Central Florida in 2008, Sitton started 112 of 121 regular-season games and all 13 playoff games he appeared in for Green Bay.
Sitton was a Pro Bowler in 2012, 2014 and 2015 with the Packers and again in 2016 in his first season with Chicago.