Smith's contract at Glasgow Warriors has not been renewed and, after a brief spell on loan at Edinburgh, the openside confirmed he plans to step away from the game.
The former Scotland U20 international made the announcement via social media, saying "This has to be one of the hardest things I have had to do in my life.
"Today I announce that I have decided to walk away from the sport that I truly love and which has given me so much joy.
"However, given the current pandemic, I have had time to really reflect and come to realise that rugby is no longer enjoyable for me and that it had become a chore to get up for training.
"I have met some of the most amazing people on my journey and come out of it with wonderful, life long friends.
"I thank all of the people who have supported me throughout my career, I would never have been able to do it without them.
"Thank you for giving me an amazing 6 years Glasgow Warriors."
The tough-tackling back-rower made his debut for the Warriors came in a February 2017 visit to the Ospreys, the first of 25 appearances in a Glasgow jersey.
Both of his tries for the club came in the same game, touching down twice in a 20-minute cameo against Zebre at Scotstoun in April 2017.
His form during the 2018/19 season saw him earn a first senior international call-up to Gregor Townsend's Scotland squad.