Kubiak fought back tears Monday as he thanked his family, Broncos owner Pat Bowlen, his coaching staff, his players, friends and a wide range of team staff members.
"This decision is strictly my decision, based on what I've been through this year and how I'm feeling," Kubiak said. "I just feel like it's time for me to do something different. Now, I'm retiring from coaching, I'm getting out of coaching, but I've got a lot to give and I'm going to find something else to do ... but it's time for me to step away from the coaching field."
Kubiak formally told the Broncos he was stepping down as coach after Sunday's 24-6 victory over the Oakland Raiders, but he deferred any public explanation until Monday. Kubiak spoke for just over 19 minutes as he prepared to leave an organization he has been with for more than two decades as a player, assistant coach and head coach.
Kubiak played nine seasons for the Broncos, was Mike Shanahan's offensive coordinator for 11 years and spent the last two as the team's head coach. Dressed casually Monday, as he often is, Kubiak even joked that he "came in wearing jeans [as a player in 1983]; I'm going out wearing jeans."
Broncos executive vice president of football operations/general manager John Elway, Kubiak's former teammate and roommate with the Broncos, said Kubiak came to him in December and said, "I need to talk to you as a friend, not my boss."
It was in a Christmas Eve discussion, at the team's hotel in Kansas City the night before the Christmas night game, when Kubiak outlined his desire to step away. Elway said he briefly tried to talk Kubiak out of the decision, including making another attempt Monday.
Kubiak added the "decision would be the same" even if the Broncos had made the playoffs.
"I know how tough this is for him to do," Elway said. "... In the long run, it's the right thing for Gary, and that's the most important thing."
After two seasons that saw the team go 21-11 and win Super Bowl 50, Kubiak cited concerns over his ability to maintain his health and do the job the way he has always done it.
Kubiak said there wasn't one specific instance that led to his decision, but rather a realization that came this season that if he stayed a head coach, he was going to have to change how he worked. Kubiak said he determined he was not going to be able that change.
"You've heard a lot about me the last week or whatever, but let me just say this: I'm doing great, I'm OK," he said. "But coaching is a very demanding business, tough business ... we all have a routine, we all have our way of going about things.
"I've always taken a lot of pride that I could coach the football team, be there for the players, be there for the coaches, be there for the organization, do a game plan, call some plays on Sunday. I've always taken a lot of pride in the fact I could do all those things, but this year I haven't been able to do that. It's been tough, and for the first time I've had to tell myself, 'Hey, you can't do that anymore.'"
Kubiak, 55, had spent a night in the hospital after the Broncos' Oct. 9 loss to the Atlanta Falcons and left the stadium that night in an ambulance. Kubiak was diagnosed with a "complex migraine condition," was away from the team for a week following his hospital stay and did not coach the team in its Oct. 13 game in San Diego.
Kubiak has said multiple times since he was trying to improve his sleep habits and had consistently deflected health questions in the weeks that followed. Kubiak also suffered what was called a "mini-stroke" in 2014 when he was the Houston Texans' head coach.
Kubiak closed his remarks, after taking a few questions, by thanking Elway, in particular, and then his wife, Rhonda. Kubiak called Elway's time with the Broncos as a player and team executive "unmatched in professional sports ... and he's the best in the business to work for. John, I love you."
To his wife, Kubiak said that Rhonda "kept me in one piece for a long time and let me go do what I wanted to do ... I'm coming home, I love you."