The 24-year-old helped Nice secure a fourth-place finish in Ligue 1 last season and becomes the Foxes' third signing of the summer for an undisclosed fee.
The Premier League champions have already welcomed Ron-Robert Zieler and Luis Hernandez to the club and Mendy is looking forward to joining the ranks.
Speaking to the club's official website, Mendy said: "I am very happy to come to Leicester City
The team have just enjoyed a great season and it's excellent to be here.
"For me I want to play at this level
I like the Premier League and I follow every match
It's fast and physical and I want to impose myself on the league."
Mendy, signed for an undisclosed fee, worked under Claudio Ranieri during a spell with Monaco and is keen to renew his relationship with the Leicester manager.
He added: "I know the coach, I know his mentality and I know his philosophy
When he speaks it's direct and clear and for me I like this."
Source : PA
Source: PA