The South African-born tighthead has been outstanding in National Division One and will be able to provide valuable cover with players such as Chris Horsman expected to be away on World Cup duty next season.
Ruwers, who stands at 6ft 3in and weighs 19st 6lbs, has enjoyed previous spells with Natal Sharks and Atlantic Pumas.
Worcester's Director of Rugby Mike Ruddock said: "We are very pleased to welcome Shaun to Sixways and we look forward to him making a big impact at the club.
"He has impressed me not only with his scrummaging skills but also with his ball carrying ability."
Ruwers said: "I'm very excited about the move to Warriors and have already been very impressed by Mike Ruddock and his ambitious plans to transform the club into a true force in the English game.
"I'm young, hungry and eager to prove I can be an asset to his club. I'm determined to take this opportunity to prove my ability in the Guinness Premiership."
Meanwhile, Tom Harding and Simon Whatling have both left Sixways as the club begins to build towards next season in the Guinness Premiership.
"I would like to thank both players most sincerely for their efforts for Worcester," added Ruddock.
"Simon has been unfortunate with injuries and the arrival of Sam Tuitupou next season means his chances would have been limited. He leaves the club with our very best wishes for the future.
"Tom expressed a desire some time ago to return home, we respect his wishes and hope he has every success in his career.
"We are now looking for potential replacements and at this moment I am considering the quality of players in our Academy programme as well as the possibility of bringing in replacements externally."