Adam Schefter of ESPN reported it's a three-year, $21 million deal with $10 million guaranteed.
Callahan was an integral part of the league's No. 1 scoring defense last season as its slot cornerback. In 13 games, the 27-year-old had two interceptions, two sacks and 45 tackles.
Pro Football Focus also noted his dominance from the slot:
A broken left foot suffered in December prematurely ended his year.
The Bears picked up Callahan as an undrafted free agent out of Rice in 2015. The 5'9", 188-pounder has 123 tackles, four sacks and 20 pass deflections in his career.
His old team may have trouble replicating its 2018 success after defensive coordinator Vic Fangio left to become the Denver Broncos head coach. Secondary coach Ed Donatell joined Fangio's staff.
The Bears also lost free safety Adrian Amos to the Green Bay Packers.
As for Callahan, he should be an excellent addition for Denver if his 2018 play is any indication, especially given that he's reuniting with Fangio and Donatell.
In a pass-happy league in which teams need solid pass-rushers and defensive backs to have any chance at stopping aerial attacks, players like Callahan are tremendous assets. He should be one for the Broncos.