The 22-year-old has long been a target for the Blues and becomes the first transfer since the appointment of new manager Jose Mourinho in what is reported to be an £18 million deal.
A statement on the club website read: "Chelsea Football Club and Bayer 04 Leverkusen have reached an agreement for the transfer of Andre Schurrle, subject to the completion of legal documentation and related matters, including personal terms and passing a medical."
Schurrle has won 24 German caps, scoring seven goals. He started his career at Mainz, scoring 20 goals in 65 appearances before moving to Leverkusen before the 2011–12 season.
The versatile attacking midfielder scored 11 league goals last season.
The deal was allowed to happen because Bayer Leverkusen have signed a replacement - Hamburg's South Korean forward Son Heung-min.
The 20-year-old Son, who was outstanding last season, signed a five-year deal with Leverkusen.
"We made it clear from the start that a transfer of Schurrle to Chelsea would only happen if an adequate sporting alternative was possible," said club boss Wolfgang Holzhaeuser.
"This alternative was now taken under contract with Son Heung-Min and so there is nothing blocking Andre Schurrle's transfer from our side."
It had been expected Chelsea midfielder Kevin de Bruyne would move on loan as part of the deal, following a successful spell in the Bundesliga at Werder Bremen last season.
However, Chelsea's statement made no mention of the 21-year-old, with Mourinho suggesting at Monday's press conference the player was very much in his first-team plans for the future.
Mourinho, who agreed a four-year deal to return to Stamford Bridge following his departure from Real Madrid, admitted it was "normal" to expect some fresh faces to be added to the squad, and Chelsea have been heavily linked with Napoli's £30million-rated frontman Edinson Cavani as well as Wayne Rooney, should the England striker be sold by Manchester United.
However, the new Blues manager, who won the Champions League for a second time with Inter Milan after leaving Stamford Bridge six years ago, maintained he was also looking to bring on the club's younger players in the new campaign.
"These 'kids' - and I say that respectfully - have big potential and big space for improvement. They've not reached their best level," he said.
"The stability the owner and I can give them is related to work - in the methods, the coaching philosophy, in my leadership, in everything that can help them improve. When you mix with them those who are over 30, we will keep a balance and try to go on."
- Sports & Recreation
- Chelsea Football Club
- Andre Schurrle
- Jose Mourinho
- Bayer 04 Leverkusen