The 30-year-old told teammates this morning of his intentions to hang up his boots after 179 matches with the Swans.
Roberts-Thomson has battled a number of injuries over the last two seasons and has played five senior matches in 2014, the last against Melbourne in round six at the MCG.
Drafted as a zone selection with pick 29 in the 2001 National Draft, he made his AFL debut in round 8, 2003 against Geelong.
Roberts-Thomson retires a dual premiership winner (2005, 2012) and also featured in the Swans’ 2006 Grand Final loss to West Coast.
Sydney Swans coach John Longmire paid tribute Roberts-Thomson’s fantastic career.
“Lewie has been an outstanding competitor for a long period of time,” he said.
“He has chased, tackled and put his body on the line countless times throughout his career.
“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.
“There is probably no greater compliment a player can be paid than being labelled a ‘big game player’, but that is exactly what Lewie was. His ability to stand up in both the 2005 and 2012 grand finals was pivotal to the outcome of those games.
“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 reached life membership of the Swans in 2012 after playing his 150th game.
Swans fans will have the opportunity to pay tribute to Roberts-Thomson this Saturday at the SCG, when he will walk a lap of honour at half time of the Swans clash with St Kilda.