Leben, 33, began his UFC career in 2005, and quickly rattled off five-straight wins before suffering his first loss within the promotion to Anderson Silva.
"The Crippler" had a tough time of it since 2011, losing five of his final six fights.
"It's been a fantastic, wonderful ride," Leben said. "I've landed more strikes than anybody out there. Definitely highs and lows, ups and downs, but I think I'm starting to realize that, for me, it might be time to make that transition away from competing and get more on the coaching side of things.
"After [UFC 168], I wanted to go back and reevaluate things, make sure that the decision wasn't based purely on emotion. That it was really what I wanted to do. And now, yes, I can say, I've really retired from competing in MMA."
Leben wrapped up his career with 22 appearances inside the UFC's world-famous Octagon, including victories over some of the top middleweights in the world.
"The bottom line, I've been with the actual UFC now for almost 10 years and I really feel like I've kind of grown with them, parallel with them," Leben said. "In this sport, you're either moving forward or you're moving backward.
"I really can't be upset. I've had a wonderful career. And again, I didn't start fighting until I was 21 years old. Back then you could actually get in the UFC, win and do well, just on being a tough guy. I was a tough guy, I had some techniques, and that always worked for me. But when you look at these guys now, like Uriah Hall, they're just a different breed of athlete than I am. The game has been evolving and changing so much, so rapidly, that I'm actually pretty happy that I can say I was in it for as long as I was in it."
Leben finished with a 12-10 record inside the UFC, including wins over Wanderlei Silva, Jay Silva and others.