The Blues have announced the England international, 27, has put pen to paper on a five-year contract at Stamford Bridge.
And he’s become their sixth summer capture following the arrivals of Alvaro Morata, Tiemoue Bakayoko, Antonio Rudiger, Davide Zappacosta and Willy Caballero in west London.
On the switch, Drinkwater said: "I’m delighted to be a Chelsea player and can’t wait to get started.
"It has been a long journey to get here but I am very happy and am looking forward to helping the club win more trophies."
Chelsea chief Michael Emenalo added: "Danny is not only a Premier League winner but also has Champions League experience which will be invaluable for us this season.
"He is a typically combative English midfielder with a cultured passing technique and his arrival significantly strengthens our midfield options."
The deal, which Leicester have revealed involves a club-record incoming fee thought to be about £35m, reunites Drinkwater with N'Golo Kante.
The duo played key roles as the Foxes marched to shock title glory under former Chelsea boss Claudio Ranieri in May 2016.
Antonio Conte will be hopeful Drinkwater can fill the void left in his squad by Nemanja Matic's departure to Manchester United.
Chelsea have bounced back from an opening weekend defeat to Burnley to win games against Tottenham and Everton.
Drinkwater is in line to make his Chelsea debut against old club Leicester on Saturday September 9.
