The three-cap England international, who won the title alongside Chelsea midfielder N’Golo Kante at the King Power in the 2015/16 season, was forced to wait until after the 11pm deadline for his move to Stamford Bridge to be finalised.
“I’m delighted to be a Chelsea player and can’t wait to get started,” the 27-year-old told the club’s media team having completed his move.
“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.”
The midfielder, who arrives as a replacement for Serbian Nemanja Matic after his move to Manchester United, has not only won the Premier League title but picked up ten appearances in the Champions League last term, reaching the quarter-finals, something which Chelsea will value highly this season.
Drinkwater was the second of two deadline day signings for Antonio Conte, with wing-back Davide Zappacosta also arriving from Torino. The Blues did, however, miss out on a deal for Swansea’s Fernando Llorente, who joined rivals Tottenham at the last minute.