Lesnar was due to enter free agency next week after his final scheduled appearance for World Wrestling Entertainment, and rumors have swirled for months that he was considering a return to the UFC when his contract was up.
Lesnar appeared on ESPN's "SportsCenter" on Tuesday night, where he broke the news that he has opted to remain with WWE and will not return to the UFC again.
"It was a very hard decision for me. The fighter inside of me wants to compete. I'm an older caveman now, so I make wiser caveman decisions. So I'm here to say that my legacy in the Octagon is over," Lesnar said.
"My legacy this Sunday in WrestleMania will not be my last. It was a hard decision to make. It took me a year to make. At the end of the day, it's all about me wanting to have fun."
Lesnar revealed that he actually has spent the past few months back in MMA training for a potential return to the UFC, but when push came to shove he began to question why exactly he was plotting a comeback to MMA.
Lesnar left the UFC in 2011 after back-to-back losses to Cain Velasquez and Alistair Overeem, and the bad taste of defeat continued to haunt him even during the following years while he was on top of the pro wrestling world as one of the biggest stars of WWE.
"For the last two months I've been training, I've been training to get back in the Octagon. I felt physically great, but something lacked mentally," Lesnar revealed. "That's not good. I talked to [UFC president] Dana [White], I talked to [CEO] Lorenzo [Fertitta], I talked to my wife, I talked to my friends. I had many sleepless nights on what to do. At the end of the day, it weighed heavily in my heart I was born to be an entertainer. I have fun doing it.
"I could go back to the Octagon — what am I going to gain? I was the UFC heavyweight champion of the world.
Due to my illness my career got cut short, and that's God's telling you it's time to move on.
As years went by it wore on me so much that the fighter inside of me didn't want it to end that way. I didn't want to leave the UFC on a losing streak. That's just the competitive guy inside me."
Before signing his new deal, Lesnar says he went to UFC 184 last month in Los Angeles to get the feeling of what it was like to be at a fight one last time just to see if he was in the right place to potentially compete again or not. In the end, his body was in perfect shape to fight again, but his mind had other ideas.
"You can't force somebody to get into the cage and fight. That's not the business," Lesnar said. "That's where I was. Was my heart and my head really into it? What are the reasons I want to get in there? Because I don’t like the way it ended or really what is it?
"At the end of the day, I'm really happy where I'm at with the WWE.
On Monday night, Lesnar appeared in Los Angeles as part of WWE's "Monday Night Raw" program as a prelude to his match this Sunday night at Levi's Stadium for the main event at WrestleMania.
He sat down with WWE owner Vince McMahon, and the two sides were able to come to an agreement on a new multiyear contract to keep Lesnar in the squared circle.
With WWE, Lesnar works a limited schedule with only so many appearances contracted throughout any given calendar year.
The schedule allows Lesnar to spend time at home with his wife and kids and not be on the road for the majority of the year like most professional wrestlers.
It was a tough decision according to Lesnar, but he's very satisified with his choice to remain with the WWE.
"The older you get, the wiser you become and I didn't want to be that guy that retired and came back. So there was a lot of different things that went through my mind.
This was a long, heartfelt decision. You weigh out the pros, you weigh out the cons," Lesnar said.
"Last night, old Vince McMahon put on the offer on the table that I couldn't refuse. It really comes down to business and money and health and well being, I've been on both sides of the spectrum. I've been in a bad position with my health. I've been in a bad position with my money. Now I'm in a great position with both and I'm happy. I love what I'm doing. I work part-time with full-time pay like everybody wants but you can't have. Just me. So I'm happy."
Lesnar, who turns 38 this year, promises that at this point his best choice was to remain with WWE and put his career in the UFC behind him for good.
"I'm officially closing the door on MMA," Lesnar said. "It was hard. I re-signed last night with the WWE. We came to a conclusion last night. The offer on the table, I just could not refuse."