It was announced on June 13 that Chelsea and Bayer Leverkusen had reached an agreement for his transfer and the 22-year-old's move to Stamford Bridge was confirmed after paperwork was completed.
He said on chelseafc.com: "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.
"I am really looking forward to it."
Schurrle, who can play as a creative wide player or central striker, will wear the number 14 shirt.
He has scored seven goals in 24 appearances for Germany, since making his debut in November 2010 while at Mainz, whom he joined from Ludwigshafener in 2009.
He signed for 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.