The Blues have long been linked with a move for the England left-back, whom Frank Lampard is a fan of, and a deal has been agreed.
Chilwell spoke of his delight at the move.
‘I am delighted to be joining Chelsea at this very exciting time for the club,” he said.
‘I’m looking forward to being a part of this young, dynamic squad led by Frank Lampard as we challenge for honours next season.
‘I can’t wait to get started and hopefully it won’t be long before we’re playing in front of the Chelsea fans at Stamford Bridge.’
In total, they have now spent £136m.
The spending could continue, too, as they continue to be linked with a £90m move for Kai Havertz of Leverkusen.