The 25-year-old began his senior career at Belgian outfit Anderlecht and joined Sampdoria back in 2016, where he made 107 appearances and scored four goals.
Praet has made three senior appearances for the Belgian national side, making his debut in a 3-1 friendly win against Iceland in November 2014.
The Foxes had to work hard to get a deal over the line before the close of play on Thursday, but managed to get the contract secured before the transfer deadline.
A statement on the club's website said: "Leicester City Football Club have agreed terms with Sampdoria for the transfer of attacking midfielder Dennis Praet, subject to Premier League and international clearance."
Praet becomes manager Brendan Rodger's fourth summer signing following the arrivals of defender James Justin, winger Ayoze Perez and midfielder Youri Tielemans.
Leicester have been hit by the loss of England centre-back Harry Maguire over the summer after he made a big-money move to Manchester United.
The Foxes were linked with bringing in a replacement, with the likes of Lewis Dunk, Nathan Ake and James Tarkowski all being connected with a switch to King Power Stadium.
However, no big signing in the heart of defence was made and Rodgers must think he has enough to cover the loss of the world's most expensive defender.
Praet will now link up with his new Leicester team-mates ahead of the Foxes' Premier League opener on Sunday against Wolves.
Meanwhile, Leicester have revealed plans that could see an expansion of the capacity at King Power Stadium.
The East Midlands outfit have brought in Legends International to oversee the market research before potentially going ahead to redevelop the stadium in the future.