Flacco, 34, was the MVP of Super Bowl XLVII in 2013 and was the Ravens' starter since 2008 until a hip injury in 2018 sent Flacco to the sidelines after Week 9. Rookie first-round pick Lamar Jackson took over for Flacco and didn't relinquish the starting role.
Teams are prohibited from commenting on the trade or the terms until it is officially processed when the new NFL league year begins March 13. Albert Breer reported the Broncos will send their own fourth-round pick to the Ravens, holding onto the fourth-round receiver from the Houston Texans in the Demaryius Thomas deal in October.
Baltimore went 4-5 with Flacco as the starter last season. Jackson led the Ravens to a 6-1 record and the AFC North title.
Hip and back injuries were concerns for Flacco in recent seasons.
Flacco has spent all 11 of his NFL seasons with the Ravens, starting all 163 of his games played. He has completed 61.7 percent of his passes for 38,245 yards and 212 touchdowns. He was the 18th overall pick in the 2008 NFL Draft.
In March 2016, he signed a three-year, $66.4 million contract extension that runs through the 2021 season. That will need to be re-worked, according to NFL Network's Ian Rapoport. The Ravens must carry Flacco's $26.5 million cap hit until June 1, per the NFL Network.
Case Keenum started all 16 games last season in his first year in Denver, which went 6-10.
Keenum, who turns 31 on Sunday, completed 62.3 percent of his passes for 3,890 yards, with 18 touchdowns and 15 interceptions. He has one year remaining on a two-year, $36 million contract, with $6.5 million of his $18 million due for 2019 guaranteed if he is released.
The misses at quarterback for Elway and the Broncos also came via the draft.
Elway has invested in three draft picks since acquiring Peyton Manning in free agency, including a second-round pick on Brock Osweiler in 2012, a seventh-rounder on Trevor Siemian in 2015 and a first-round pick -- via trade up -- on Paxton Lynch in 2016.
--Field Level Media