Kubiak, fighting back tears at his press conference Monday morning, said he is "retiring from coaching" due to health concerns.
"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 said isn't stepping away because of any specific medical problem.
"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," Kubiak told reporters. "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.'"
John Elway, the Broncos' executive vice president of football operations/general manager, made the announcement earlier Monday, releasing a statement.
Kubiak told players and staff after Sunday's season-ending 24-6 victory over the playoff-bound Oakland Raiders that he was stepping down for health reasons from the job he took two years ago.
Kubiak endured another health scare earlier this season.
"As I told our team last night, this is an extremely difficult decision to step down as head coach," Kubiak said in his statement released by the team. "I love to work and I love football, but ultimately the demands of the job are no longer a good fit for me.
"I gave everything I had to this team the last two seasons, but this year, in particular, has been tough on me. As hard as it is to leave this position, I know that it's the best thing for myself, my family and the Denver Broncos.
"I've been blessed to spend more than two decades with the Broncos working for Mr. Bowlen and a great organization from top to bottom. I'm forever grateful to this team, in particular John Elway and (president and CEO) Joe Ellis, for giving me the opportunity to serve as its head coach. There are countless others to thank, including players, coaches, personnel staff, trainers, support staff and fans.
"Although we fell short of our goals this year, I'm proud of our teams these past two seasons. Helping to bring Mr. Bowlen, his family and this organization its third Super Bowl is something that will always be very special to me. I'm not sure what my future holds, but I know that I'll always consider myself a Bronco. This team is in good hands with a lot of outstanding people, and I expect great things ahead for the Denver Broncos."
This season took a toll on the 55-year-old coach after a second health scare on the job.
Kubiak left the Broncos for a week in October, missing a Thursday night game in San Diego for what the team called a "complex migraine condition." In 2013 while Kubiak was head coach of the Houston Texans, he collapsed during a game against the Indianapolis Colts after suffering a mini-stroke and had to be rushed to the hospital.
Elway, who brought his former backup back to coach the team they both played for, will begin searching for a replacement immediately.
"When Gary informed me of his decision to step down as head coach, I was obviously saddened and disappointed," Elway said in a statement. "But, I understand and respect Gary for doing what's right for him as well as his family.
"From the time he was hired as head coach, Gary worked to get the most out of the players to push this team over the top. He gave everything he had, and we won a lot of games along the way. The way Gary led the team and managed a challenging situation during our Super Bowl run was one of the best coaching jobs I've ever seen.
"Gary's been a teammate, co-worker and, most importantly, a friend for more than 30 years. Without a doubt, he's left the Broncos in a better place than when he stepped off that plane from Houston two years ago. I appreciate all Gary has done for us. On behalf of our entire organization, I thank him and wish him all the best."
Kubiak, hired as the 15th head coach in franchise history on Jan. 19, 2015, helped the Broncos to the second-most wins in the NFL in his two seasons with a 24-11 (.686) record.
During the 2015 season, Kubiak became only the fourth head coach in NFL history to lead a team to a Super Bowl victory in his first year with the Broncos' 24-10 win over the Carolina Panthers in Super Bowl 50. His 15 overall wins (12-4 regular season, 3-0 playoffs) in 2015 were the most in Broncos history by a coach in his first year with a team and helped Denver to an AFC West title along with the No. 1 overall AFC playoff seed.
Sunday's win over the Raiders allowed the Broncos to finish with a winning record (9-7), though it wasn't quite good enough to earn a postseason berth, where they would have had a chance to defend the Super Bowl title.
In 10 seasons as an NFL head coach (Denver, 2015-16 and Houston, 2006-13), Kubiak has a career coaching record of 87-77 (.534). He has spent 22 years with the Broncos (nine as a quarterback from 1983-91; 11 as offensive coordinator from 1995-2005) and coached on the franchise's back-to-back Super Bowl champion teams from 1997-98.
Kubiak said Monday he wasn't sure yet of his future plans, except spending more time with his wife Rhonda.
"I'll find something," Kubiak said. "I'll find another passion. There's a lot of things to do in life."