The 22-year-old moves to Stamford Bridge from the Bundesliga club, whom he joined back in 2011, following the completion of legal documentation and related matters, including personal terms and a medical.
It was announced on June 13 that Chelsea and Leverkusen had reached an agreement for the transfer but formalities have finally been completed with Schurrle given the club's No 14 shirt.
After representing Germany at both U19 and U21 level, the young attacker earned his first call-up to the senior squad in November 2010, while at Mainz, whom he joined from Ludwigshafener in 2009.
He was handed his debut as a late substitute in the friendly against Sweden and has scored seven goals in 24 appearances for his country.
In his first season with Leverkusen he scored nine times in 40 appearances and last term he netted 14 in 43 and told the Chelsea website: "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 becomes effectively Chelsea's first signing since Jose Mourinho returned as manager at Stamford Bridge to replace interim boss Rafa Benitez.
Speaking earlier this month after the deal had been agreed, Schurrle expressed his determination to shine and his intention to become a regular in the team, unlike German compatriot Marko Marin, who endured a frustrating first season at the club.
"I first met Jose Mourinho at Michael Ballack's farewell game in Leipzig last week," Schurrle said in The Sun. "He was in charge of my team, the World Select side.
"We met before the game, he shook my hand and told me 'Everything has gone through, and you are my player'. That was a wonderful feeling.
"My first impression of him was that he truly has a special personality. He is a cool guy as well.
"I spoke about him with my national team-mates Sami Khedira and Mesut Ozil, who have played under him for Real Madrid. They both told me he is the best coach they have ever worked with.
"I don't fear suffering the same fate as Marko and just being a replacement. I will try to make my way at Chelsea."
Leverkusen had agreed to let Schurrle go following the signing of Heung-min Son from Hamburg after the inclusion of Kevin de Bruyne in part exchange had reportedly been blocked.