Keenum, who has also had unsuccessful stints with the Texans and Rams, went 11-3 in the regular season as a starter for the Vikings, throwing for 3,547 yards and 22 touchdowns with just seven interceptions.
The 30-year-old will look to help steer the Broncos to a bounce-back season after they went 5-11 in 2017.
And while the Broncos do need a new quarterback, is Keenum the answer?
The Broncos had three quarterbacks start games this past season - Trevor Siemian, Paxton Lynch and Brock Osweiler - but it was a bumpy ride on offense as the Broncos were among the league leaders in turnovers and offensive coordinator Mike McCoy was sacked in November.
Manning had a spectacular closing chapter in Denver, leading the Broncos to the playoffs in all four of his seasons, reaching two Super Bowls and winning one.
At the scouting combine, two weeks before the start of free agency, Elway did compare the "fluid" nature of chasing a quarterback in free agency this year to the pursuit of Manning.
After sitting out the playoffs in each of the last two years following their Super Bowl 50 triumph, the Broncos have apparently found their next signal-caller.
At the National Football League scouting combine this month, Elway said, "we'll continue to look at all of the options out there when it comes to quarterback".
Denver were also reported to be in the hunt for Cousins having struggled through three options under centre last season but general manager John Elway has made his move for Keenum. Their inconsistent play on both the offensive line and at quarterback have been big reasons why they've sat out the postseason.
"I still think that we're not too far away", Elway said earlier in the offseason. We didn't play very well there previous year, and that's not all on the players.