The Brazilian made the announcement on his Twitter account, and was later verified by separate sources.
Rua lost the fight to Watson in England after a one-sided match ended with the Brit knocking out the former EliteXC champion.
The loss brought Rua’s record to 20-12-1 overall.
“I would like to announce officially my retirement from pro MMA fights tonight. It was an amazing run, and it’s a very tough moment,” Rua wrote. “But there comes a time for all in life, and it’s time to move on. I am proud of all I did in MMA and all experiences I had.”
During his career, Rua fought in several different organizations including Pride, Dream, and Cage Rage, as well as spending time as EliteXC middleweight champion.
Rua will continue to teach and train alongside his brother Maurcio “Shogun” Rua, and said he looks forward to spending more time with friends and family.
“It was a fantastic road and this is a very trying time. But there comes a time for everything in life, and ‘s time to move on. I’m proud of everything I’ve done in MMA and all the experiences I had in this profession that I embraced with love,” Rua stated.
“I’ll keep working on MMA giving seminars, lectures, training athletes, and doing my part to help our sport that I love so much. Now it’s time to help others, and enjoy my family, my wife, my children, and move on.”
Rua is the latest of a string of fighters that have announced retirements recently. Just over the last two months both Ricardo Almeida and Nick Thompson have called it a career as well.