Chelsea complete Schürrle signing
The two clubs reached an agreement for 22-year-old earlier this month, and he becomes the first signing under returning manager Jose Mourinho.
No transfer fee was disclosed.
"I am so happy now I have signed and it is an honour for me to play for this club, with this team and for these great fans," he told the club's website.
He has scored seven goals in 24 appearances for Germany and netted 11 times as Leverkusen finished third in the Bundesliga last season.