Hazard follows in the footsteps of Lille team-mate Cole in signing for Chelsea, with the England international having done so eight years ago.
Cole had some kind words to say about the club, and that also helped Hazard make his decision.
"As somebody who loves the club himself, he said he could really see me in the shirt, so when I see him next I'll tell him he was right.
"It's a dream come true for me. I can't wait to get started and for the season to start so I can meet my new team-mates, the supporters and all the people who are involved."