In only the third time since the award began in 1957, the two quarterbacks each received 16 votes from a nationwide panel of 50 writers and broadcasters who cover the NFL.
"It is great," McNair said. "My words can't express how I feel being co-MVP with another great quarterback like Peyton. It's very emotional right now for me that people look at me as being one of the top quarterbacks of the NFL, one of the top players, and a co-MVP."
Said Manning: "To be sharing it with Steve, a player I have the most respect for and who has had a tremendous year, and to be ahead of guys like Tom Brady, who's a friend of mine, and Jamal Lewis, a former teammate of mine at Tennessee who easily could have been there, as well, it's tremendous."
Brady, the New England Patriots' quarterback, finished third with eight votes, followed by Baltimore Raven running back Lewis, the AP Offensive Player of the Year, with five.
The other players to share the MVP award were Green Bay quarterback Brett Favre and Detroit running back Barry Sanders in 1997 and Philadelphia quarterback Norm Van Brocklin and Detroit linebacker Joe Schmidt in 1960.
Quarterback Jon Kitna, who helped keep the Cincinnati Bengals in playoff contention until the final week of the season, was named the Associated Press Comeback Player of the Year.
Kitna, who finished second in the AFC with 26 touchdown passes, received eight votes. Dallas quarterback Quincy Carter was second with seven, followed by Baltimore tackle Orlando Brown, with six. Carolina running back Stephen Davis and Kansas City safety Jerome Woods had five each.
Former New York Giant coach Jim Fassel and Washington Redskin owner Dan Snyder have concluded more than 12 hours of talks over two days in San Francisco.
Snyder plans to talk to former Minnesota coach Dennis Green and Seattle defensive coordinator Ray Rhodes. He is looking for a replacement for Steve Spurrier, who resigned on Tuesday.
Six Green Bay Packer starters who had been bothered by injuries returned to practice: receivers Donald Driver and Robert Ferguson, cornerbacks Mike McKenzie and Al Harris, linebacker Na'il Diggs and nose tackle Gilbert Brown.
But defensive end Chukie Nwokorie, who has a cracked bone in his right wrist, remained sidelined and won't play Sunday against the Seattle Seahawks in a wild-card playoff game.