After his 2013 season was all but wiped out by a serious knee injury, Roberts-Thomson has played just five games this season, spending the past six weeks in the NEAFL.
Influential in attack in 2012, he has been unable to break into a star-studded forward line that includes Lance Franklin, Kurt Tippett and Adam Goodes.
The cult hero leaves the game after playing a crucial role in the 2005 and 2012 premierships, playing 179 games after being recruited as a zone selection with pick No.29 in the 2001 National Draft.
Coach John Longmire said the 30-year old had been a big game player, playing a pivotal role in the 2005 and 2012 Grand Finals.
"'Lewie' has been an outstanding competitor for a long period of time," Longmire said.
"One of his great assets has been his ability and willingness to adapt to any role he has been given.
"There is not a position on the ground that Lewie hasn’t played in over the course of his career."
"LRT has been a fan favourite – perhaps even a cult figure – and I’m sure all our fans are thankful for his wonderful contribution to this club."
Roberts-Thomson will walk a lap of honour at half time of the Swans' clash with St Kilda at the SCG on Saturday.
So @Lewie_RT has a few extra admirers at his retirement press conference pic.twitter.com/FXfpGYxbjj
— James Dampney (@AFL_JD) August 14, 2014