Stann, 32, made the announcement during a special broadcast of Ariel Helwani's "The MMA Hour."
He said he opted to retire because he wanted to be fully healthy and didn't want to suffer head trauma. When he was violently knocked out by Wanderlei Silva in Japan on March 3, Stann began seriously thinking of walking away from the game.
He has two daughters and a third on the way and didn't want to risk suffering any long-term brain trauma.
Stann was an American football player since he was a child and went on to play for the Naval Academy. He also won a Silver Star for heroism while a Marine Corps captain and had fought professionally since 2006.
He spent much of his life taking blows to the head and finally came to the realisation that enough is enough.
"After playing football for this many years, and being involved in several explosions in Iraq and now fighting professionally for [almost] eight years, I definitely am rolling the dice with my long-term health," Stann told Helwani. "I've not had any issues with head injuries. I don't have a number of documented concussions. But these are issues where you don't know there is something wrong until there is something wrong.
"Bringing my third child into the world this fall, my third daughter, it is not a good idea for me to roll those dice. I've had the opportunities to get to the highest level of the sport. I've fought some of the best fighters in the world and, unfortunately, I've lost a bunch of those fights. That has stopped me from getting to the level I would like to get to in the sport. I do think I could continue, but if I were to continue, and try to revamp myself as a fighter, I think I'd run the risk of long-term health problems."
No MMA promoter could have scripted Stann's retirement speech better. Though the sport has detractors who simply don't understand it, MMA has been proved through medical studies to be safe as far as combat sports go and relatively free of traumatic brain injury.
Part of that is because of the nature of the sport – it doesn't only involve kicking and punching to the head, but also wrestling and jiu-jitsu that don't lead to brain injuries – but, frankly, part of it is that the sport is young and not a lot of fighters have been around to be studied.
There are numerous cases of so-called "punch drunk" boxers who clearly have taken too many blows. And in the NFL, concussions have become a significant issue.
By announcing his retirement while in his physical prime, Stann sent a very strong message to his peers that health, not glory, is the long-term objective.
MMA fighters are, as a whole, a group of bright and thoughtful people. But the sport's culture is to be "a warrior" and there is a lot of pressure to engage in toe-to-toe slugfests.
Over time, too many of those slugfests that bring the fans out of their seats will impact the fighter's brain functions.
Stann, one of the toughest men in arguably the toughest sport in the world, showed that it is OK to walk away by making his retirement announcement.
He made a lot of money in the sport, developed contacts and then used those contacts to help him get a job as a broadcaster that will help ease his transition into retirement.
After leaving the Marine Corps, Stann started a company, Hire Heroes, that was designed to help veterans find jobs. He worked full-time in that position throughout his career.
Fox hired him to do analysis on its UFC broadcasts and recently announced that he will be a color commentator on ACC football broadcasts.
Stann, thus, did it the right way: He got out of the sport what he could, used it to help build a long-term career and retired before he had any health issues.
He was a fun fighter to watch and always took seriously the responsibility as an athlete to give the fans value for their money.
But his biggest accomplishment is, undoubtedly, leaving a legacy for other fighters to follow: Use the sport, and don't let it use you. Walk away when it's time. And don't ever risk your long-term health for the sake of a cheering crowd.