After signing a five-year contract, Kante said: "I am so happy to have signed for one of the biggest clubs in Europe. It’s a dream come true for me.
"The opportunity to work with Antonio Conte, a brilliant coach, and some of the best players in the world was simply too good to turn down.
"My first season in English football was very special and now I hope to go on to achieve even more during my time as a Chelsea player. I am looking forward to meeting up with my new team-mates and helping the club achieve a lot of success."
Sky Sports' Rob Dorsett reported Kante's deal will net Leicester £32 million.
Kante was one of the standout men in the Foxes' stunning title win in 2015-16. Manager Claudio Ranieri brought the player in from Caen in the summer of 2015 after he impressed in Ligue 1, although few would have anticipated that the midfielder’s upward trajectory would be so steep.
The France international was the best midfielder in the Premier League as Leicester romped to the title. Kante's performances at the heart of the Foxes team were staggeringly efficient, as he covered an amazing amount of ground and used razor-sharp defensive instincts to halt opposition attacks.
These numbers from Squawka Football show just how difficult opponents found it when coming up against the 25-year-old:
They’re attributes that Chelsea will be delighted to tap into. Players in midfield who are energetic and defensively minded are easy to find, but getting someone to carry out that duty with the same distinction as Kante is tough.
New Blues boss Antonio Conte demands intensity in all sections of the pitch, too. At Juventus and more recently with Italy, he's fashioned relentless sides, and at the team's core, having someone like Kante alongside Nemanja Matic would give the Blues a foothold in many midfield battles.
Additionally, Chelsea supporters will also see how effective the Frenchman is at converting defence into attack. For a footballer of such a small somatotype, Kante has a loping stride and breathtaking pace, something that was key to Leicester being a devastating counter-attacking force throughout the 2015-16 season.
The challenge for Kante will be replicating these standards with more talented players around him. At Leicester, he epitomised the way the team operated, as they were dogged off the ball and incisive on it. Chelsea don’t operate in quite the same style, but the Frenchman will find a way of making a positive impact on the way they play.