The 27-year-old Belgian has penned a three-year deal at Villa Park and joins the club for an undisclosed fee.
De Laet tasted double success last season, having helped Leicester win the Premier League title while also being part of the Middlesbrough squad that won promotion to the top flight.
He spent the first half of the campaign at the King Power Stadium, making 12 league appearances for the title-winning Foxes, before joining Championship side Boro on loan in February.
Villa manager Roberto Di Matteo said: “I’m very pleased to have brought Ritchie to the club.
“He is another player who not only has Championship experience but has also played a part in helping a team win promotion back to the Premier League.”