The 20-year-old joined Chelsea in January from Racing Genk, with the plan that he would be loaned out this summer.
De Bruyne will spend the 2012/13 season at Bremen after ending last term on loan at Genk from Chelsea.
Bremen have no option to make the move permanent with De Bruyne highly regarded at Stamford Bridge.
The Belgium international will ironically help fill the void left by Marko Marin’s switch to Chelsea.
Bremen’s general manager Klaus Allofs confirmed the signing of De Bruyne after the Belgian successfully came through a medical.
“We have Kevin for several months,” Allofs told the club’s official website. “We are glad that we can increase the quality in our squad with this commitment.”
De Bruyne was happy to make the move to Bremen for next season, saying: “It’s great the move to Bremen is done.
“Werder has a great tradition, playing in one of the best leagues in Europe with a full stadium and I want, with my new team-mates, successful football.”