The 55-year-old joined the Broncos in January 2015 and helped the team to a 24-10 win over the Carolina Panthers at Super Bowl 50 in what was the final game of Peyton Manning's illustrious career.
However, nine wins from their 16 matches in 2016 saw them miss out on the playoffs, and Kubiak announced his retirement earlier today following last night's 24-6 victory over the Oakland Raiders.
Concerns had been raised over Kubiak's health after he was hospitalised and missed a match with a complex migraine earlier this season, having also collapsed during a game while in charge of the Houston Texans in 2013, but he insists that he is not stepping down for health reasons.
"You've heard a lot about me the last week, but let me just say I'm doing great, I'm okay. But coaching is a very demanding business, a tough business. It's been tough and for the first time I've had to tell myself that you can't do that any more," he told reporters.
"I've struggled big time this year. So this decision is strictly my decision, based on what I've been through this year and how I'm feeling, and I just feel it is time for me to do something different.
"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 and I'm going to wake up with that same passion as when I was coaching, but it's time to step away from the coaching field."
Kubiak, who has spent 22 years with the Broncos during his playing and coaching career, added in a statement: "As I told our team last night, this is an extremely difficult decision to step down as head coach. I love to work and I love football, but ultimately the demands of the job are no longer a good fit for me.
"I'm not sure what my future holds, but I know that I'll always consider myself a Bronco. This place is special, and it's built to do one thing - it's built to win championships and it's in a great place. And it's going to win many more."
Kubiak also spent time with the Texans and the Baltimore Ravens during his coaching career.