He signed for Bayer Leverkusen at the end of the 2010/11 season.
In his first campaign he scored nine times in 40 appearances and last term he netted 14 in 43 to earn his move to Stamford Bridge.
Schurrle knows Chelsea well, having watched from afar.
"I wanted to come here so I think I watched every single Chelsea game (last season)," he said.
"They finished the season very strongly; finishing third was very important for the club, qualifying for the Champions League without having to go through the qualifiers, so the last month in particular was very good."
"Wide on the left is my best position because I can cut inside and score goals with my right foot, which I hope to be able to do here, but I am confident playing anywhere offensively," Schurrle added.
"They are all great players, very young with lots of quality. It was my dream to train every day with such talented players so I'm very much looking forward to it."