Midfielder Marin will join the Blues in the summer after agreeing terms on a five-year deal.
Marin, who joined Bremen from Borussia Monchengladbach in 2009 and was contracted to the club until June 2013, has already passed a medical in London and will sign a contract with the Blues in the next few weeks, according to his current club.
Marin said: ‘I had a really good time with Werder together with many great guys here, and I have lots of nice memories, but of course I am looking forward to the challenge of playing in the Premier League with such an established club.’
Marin made his Germany debut in 2008 and was part of their 2010 World Cup squad.
However, he has spent much of this season on the sidelines due to injury and is not assured of a place in Joachim Low’s squad for Euro 2012.
Bremen’s director of sport Klaus Allofs said 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 and we had good talks with the management at Chelsea, so that we were able to reach an agreement quickly.
‘In the coming weeks, we will then deal with the last formalities. We wish Marko all the best for this new challenge.’
Reports in Germany also claim that Chelsea striker Romelu Lukaku will spend a season on loan with the Bundesliga side as part of the deal.