Williams was part of the British men's lightweight four that finished runners-up at the London 2012 Olympics alongside Northern Ireland brothers Richard and Peter Chambers and Chris Bartley.
After the Games Williams went to work as a trader for Goldman Sachs and has decided to continue with the job, ending his association with rowing.
"Ultimately, I feel very fortunate to have had such an enjoyable career, making some good mates and winning a solid handful of medals, all of which culminating in a fantastic summer in 2012," he said.
Williams travelled to the Beijing Olympics in 2008 as a reserve before winning the lightweight men's four world title two year’s later on New Zealand's Lake Karapiro with Richard Chambers, Bartley and Paul Mattick.
"Rob converted his significant talent in our sport to great effect and was exceptional in combining his PhD with his rowing, demonstrating that he always remained conscious of the world around him. He will be a great asset to his employers and we wish him well with the future", said Sir David Tanner, GB Rowing Team Performance Director.
© Sportsbeat 2014