The Glasgow Warriors player sustained a career-ending neck injury in a collision with Lions full back Lee Byrne during last year's Six Nations encounter between Wales and Scotland.
Evans suffered a slipped neck vertebra and has since undergone two neck operations. Despite those operations being successful, the 24-year-old has been advised to give up the sport and has confirmed the long-expected news.
"I can still do pretty much anything. I just can't play a physical game such as rugby," said Evans.
"When you're told you can't play the sport you love dearly, it comes as quite a shock.
"I've been fortunate to have played six seasons at the top against some of the best players in the world. I'll have those memories for the rest of my life.
"You can ask any rugby player who has had a freak accident and they will still tell you that rugby is the best game in the world.
"Even though I can't play the game, I'll still be as enthusiastic off the pitch as I was on it.
"No matter what the future holds, I know I will remain a big follower of my brother, Max, Glasgow Warriors and the Scotland team for the rest of my life."
Scotland head coach Andy Robinson voiced his support for Evans.
"Thom is a talented and resilient lad and, whatever challenges he decides to take on, he does so with our full backing and knowing that the rugby family will always be there to support and encourage him," he said.