"There's just something about 18 years, 18 was a good number," Manning, fighting back tears, said while winding down his opening statement, chronicling his rookie season and an on-field handshake with childhood idol Johnny Unitas.
Manning thanked fans from two NFL cities -- Denver and Indianapolis -- and the University of Tennessee, and quoted biblical scripture from the Book of Timothy when he paraphrased "I fought the good fight. I finished the football race. And it is time."
His retirement will clear $19 million in salary cap room for the Broncos. Manning spent the past four seasons with Denver after 14 with the Colts, and is almost certain to inducted into the Pro Football Hall of Fame when he becomes eligible in five years.
Manning was a five-time NFL MVP and won 200 games, including the postseason, and claimed his second Super Bowl ring in Super Bowl 50 in February. Manning was a 14-time Pro Bowl selection.
Manning, who turns 40 on March 24, retires as the NFL's all-time leader in passing touchdowns (539), passing yards (71,940) and quarterback regular-season wins (186, tied with Brett Favre).
Manning said he wanted to spend reflective energy enjoying that final game starting the offseason in a good mood for only the second time before deciding last week to retire. He said he knew it was just the right time.
Manning said it was hard to say what he would do next to scratch the competitive itch that drove him to greatness.
"I haven't ruled anything out. I have made no decisions," Manning said. "I'm going to go on another vacation after this. I'm going to play some golf with my two brothers."
With the Broncos at 7-2, head coach Gary Kubiak said he told Manning after a poor first half against the Kansas City Chiefs it was time for him to focus on his health. Manning was playing with a torn plantar fascia in his foot and was placed in a cast for two weeks while Brock Osweiler stepped into the starting lineup.
Denver gave Manning a second NFL life following spinal fusion surgery that led to his release from Indianapolis. The Colts drafted Manning first overall in 1998.
"Grateful is the word that comes to my mind when thinking of the Denver Broncos," Manning said. "To all of my Denver teammates, thank you for what you've done for this old quarterback."
Broncos executive vice president of football operations and general manager John Elway said Manning "revolutionized" the game with his work at the line of scrimmage.
"There's not a guy in the NFL who can walk away and say I've done everything that could possibly be done. Peyton Manning can say that," Elway said Monday. "Four years ago, when the unimaginable happened -- Peyton Manning was going to be a free agent -- at first, did I think we had a shot? No, especially from where we were coming from.
"Fortunately, we got the first call in. From that day in, look at what we've done the past four years. A lot of that has to do with this guy. He made my job easier. What he was about. The way he went about it. Guys knew if he was on the team, we had a chance."
Kubiak shared some personal moments during Manning's press conference.
"As a coach we get reminded all the time about the shield. Protecting the shield, integrity," Kubiak said. "There was no greater example of that."
Manning battled injuries and missed six games in 2015 after also encountering health issues late in the 2014 regular season.
With Manning's retirement, the Broncos reportedly have offered backup quarterback Brock Osweiler a three-year contract worth more than $45 million. Unless the sides reach a new deal, Osweiler will become a free agent Wednesday.
Osweiler, 25, showed promise in eight appearances last season, throwing for 1,967 yards while completing 61.8 percent of his passes with 10 touchdowns against six interceptions. He went 5-2 as a starter after a left foot injury forced Manning to the bench.
"The Union of NFL Players congratulates Peyton Manning on a tremendous career of leadership and for how he changed the game on and off the field," NFLPA executive director DeMaurice Smith said in a statement. "Players of every generation should know him as someone who cared deeply not just about the football, but about the people who have made the sport what it is today. From his dedication to the history of the game to his decision in 2011 to stand up for the rights of every player, past, present and future, we know that he will continue to be an example to others long after his playing career."