The move also includes undisclosed NFL draft considerations. A league source told ESPN's Ed Werder that the Ravens will get Denver's 2016 fourth-round pick in exchange for Gradkowski and Baltimore's 2016 fifth-round selection.
Gradkowski was the Ravens' starting center in 2013 but was the worst-graded player at that position by Pro Football Focus. The Ravens traded for Jeremy Zuttah last year, and Gradkowski was buried on the Ravens' offensive line depth chart. He played sparingly, appearing in just eight games.
Broncos coach Gary Kubiak and offensive coordinator Rick Dennison obviously saw something they liked in Gradkowski, who did start 16 games for the Ravens in 2013. Kubiak was the Ravens' offensive coordinator last season, while Dennison was the team's quarterbacks coach.
Dennison, however, was the Broncos' offensive line coach during much of Mike Shanahan's tenure as head coach when Kubiak was the team's offensive coordinator.
The center job is open for the Broncos and the two top candidates on the depth chart before Wednesday's trade were Manny Ramirez, who was moved out of the center job nine games into the 2014 season, and Matt Paradis, who spent his entire rookie year in '14 on the team's practice squad.
The Broncos did sign guard/center Shelley Smith in free agency -- Smith had played for Kubiak with the Texans -- but Kubiak has said he wants to keep Smith at guard in the Broncos' offensive line rotation.
Gradkowski was a fourth-round draft pick by the Ravens in 2012 and will be in the final year of his rookie deal. Gradkowski is scheduled to count $1.542 million against the salary cap in 2015 with a $1.663 million base salary.
ESPN.com Ravens reporter Jamison Hensley contributed to this report.