The two clubs have settled on an undisclosed fee for the 23-year-old, who has agreed personal terms with the Blues will join the club in the summer.
Marin, who was born in Bosnia and Herzegovina before moving to Germany with his family at an early age, said: “I had a good time with Werder but I am looking forward to the challenge of the Premier League.”
Marin has scored 12 goals in 87 Bundesliga appearances for Werder Bremen and also played in the 2010 German Cup Final, when his side lost to Bayern Munich.
The Germany international has made 16 appearances for his country, scoring one goal since making his senior debut in May 2008.
Bremen’s director of sport Klaus Allofs added in a statement: “We have always said that we would be open to talk if any of our players receives a good offer which was also interesting for Werder.
“In the coming weeks, we will deal with the last formalities. We wish Marko all the best for this new challenge.”
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