The award, first won by Roger Bannister in 1954, is given for "superior athletic achievement."
Manning, who missed the 2011 season following a series of neck surgeries, moved from Indianapolis to Denver for 2012 and led the team to a 13-3 record. The Broncos this season are tied for the best record in AFC at 11-3.
Manning has completed 393-of-580 passes for 4,811 yards and 47 touchdowns. He is 665 yards off the NFL record (set by Drew Brees in 2011) for passing yards in a season and three touchdown passes off Tom Brady's 2007 record of 50.
Denver leads the NFL in several offensive statistical categories, including total offense, passing and points scored.
"At first, when I knew we were considering Manning, I thought: good choice. Lifetime-achievement-award choice," SI Senior Writer Peter King said in a release. "But if you isolate this year, you're looking at a player two years removed from four neck procedures that would have prompted many 35-year-old legends to choose retirement.
"He has his Super Bowl. He has his MVPs. Now he's on the verge of breaking the most important single-season quarterback records in the 94-year history of the game. He threw seven touchdown passes against the defending Super Bowl champs. And he's got his team set to win the top seed in the AFC.
"Who plays his best -- wounded, with so many great young guns chasing him -- at 37?"
Manning is the eighth football personality to win the annual honor. Six of those have been record-setting quarterbacks, starting with Terry Bradshaw in 1979. Other NFL quarterbacks to have won the award are Joe Montana in 1990, Brady in 2005, Brett Favre in 2007 and Brees in 2010.