Known for a steady, guiding hand in developing his athletes, he was nicknamed "The Coach."
His death was confirmed by Mike Straka, a friend of Tompkins' who worked with him at TapouT.
Straka told MMA Fighting that Tompkins was in Canada at the time of his death with his brother-in-law Sam Stout and longtime fighter Mark Hominick. The cause is unknown pending an autopsy.
Tompkins' wife Emilie was in Las Vegas, where the couple lived.
Late Sunday night, she released a statement on her husband's passing. It read:
"Team Tompkins thanks everyone for all of the condolences that have come in since the tragic news of 'The Coach's' death. Shawn would be touched beyond words by the outpouring of love from the MMA community. Sam Stout, Chris Horodecki, Mark Hominick, Kekoa Quipolta, Mr. and Mrs. Tompkins and I thank you for the respect you have shown us during this trying time. Shawn loved MMA and he considered all of you family. We will miss our Coach very much."
An Ontario, Canada native, Tompkins fought as a professional mixed martial artist, but never won, going 0-4. But it was as a trainer that he made his mark in the sport, helping notable fighters like Stout, Hominick and Chris Horodecki to the big leagues.
As a trainer at Xtreme Couture, Tompkins was in the corner of Randy Couture for several of the legend's fights.
In 2009 though, he struck out on his own, leaving Xtreme Couture and moving to the newly opened TapouT gym in Las Vegas, where he was the head trainer. He also worked with former UFC light-heavyweight champion Vitor Belfort for several bouts.
More recently, he had worked with Hominick prior to his featherweight title loss to Jose Aldo at UFC 129.
Tompkins' death cast a pall of sadness over Sunday's UFC Live event in Milwaukee, as word of his passing spread as the main card was about to begin.