The deal, which was first reported by ESPN, is for a fourth-round draft pick, a source told the AP.
The trade cannot officially be processed until the new NFL year begins March 13.
By moving on from Flacco, who has played his entire 11-season NFL career in Baltimore, the Ravens are committing fully to second-year quarterback Lamar Jackson.
Flacco, 34, led the Ravens to a victory in Super Bowl XLVII in 2013, earning MVP honors for his performance in the 34-31 win over the 49ers
For Denver, the trade means they are moving on from Case Keenum, who signed a two-year, $36 million deal in free agency last offseason. Keenum is due $18 million this upcoming season, but only $7 million of that is guaranteed.