Andrew Mason of DenverBroncos.com provided word of the decision, noting head coach Gary Kubiak met with Manning and backup Brock Osweiler prior to telling the team during a morning meeting.
At a press conference, Kubiak told reporters the decision to start Manning is "best for our football team."
Manning, 39, had perhaps the most challenging season of his entire career. He struggled with injuries and inconsistency, eventually losing his starting job to Osweiler midway through the season. In 10 appearances, Manning threw for 2,249 yards, just nine touchdowns and 17 interceptions while completing 59.8 percent of his passes.
Osweiler struggled in the season finale against the San Diego Chargers, however, after throwing two interceptions and fumbling. While Manning only went 5-of-9 with 69 yards in relief, he led the Broncos on four scoring drives and to a victory that earned them the top overall seed in the postseason.
After the game, Kubiak noted that he went with Manning in the third quarter of that game because of a gut feeling.
"Sometimes, the feel is that the team is just looking around that guy, for that tremendous leadership type of stuff," Kubiak said after the game, per Jeff Legwold of ESPN. "That's what I felt."
On Thursday, Kubiak said: "We think the world of Brock. He's done a hell of a job."
It would appear that Kubiak's gut is telling him that Manning is the best option for the team in the postseason, too. It's a risk, considering Manning's shaky form this season and his long injury layoff, but ultimately his intelligence and veteran leadership made him the choice.
The presence of Osweiler means that Manning will have a very short leash, however.