The 19-year-old featured for the Blues in their pre-season friendly agaisnt Barcelona and he has now completed his move to Stamford Bridge.
“I am very happy to complete my transfer to Chelsea,” he told the club’s official website.
“It is an exciting time for me to join the English Premier League champions and I hope I can become an important player for the club,” he added.
“I very much enjoyed my time with the squad during pre-season and I am very grateful to Fluminense for allowing me this opportunity.”
Kenedy will wear the No.16 shirt at Chelsea.