"Bringing Danny back is a key re-signing for us," Bears general manager Ryan Pace said in a statement. "Not only is he a great inside linebacker and great leader on our team, he is a big part of our culture. We are proud to have him under contract in Chicago for three more seasons."
Chicago opted to retain Trevathan even though fellow inside linebacker Nick Kwiatkoski, 26, also is set to become an unrestricted free agent. Kwiatkoski is expected to generate substantial interest in free agency when the new NFL league year begins on Wednesday.
Trevathan, who turns 30 years old on March 24, has started 45 regular-season games for the Bears since he signed with them in free agency in 2016.
When healthy, Trevathan thrived in the middle of Chicago's defense and recorded 102 tackles, two interceptions and eight tackles for loss in 2018.
However, Trevathan frequently struggled with injuries and missed 16 games for the Bears over a four-year stint, including seven last season because of a gruesome elbow injury suffered in Week 10 against the Detroit Lions.
"He's such a great leader," Pace said at last month's NFL combine. "He's such a good player. Obviously, when he was hurt last year that hurt our defense for a multitude of reasons. But he's an important part of what we're doing."
Originally a sixth-round pick out of Kentucky, Trevathan spent the first four years of his career in Denver, where he played a large role on the Broncos' Super Bowl 50 championship defense.