Villa have played an undisclosed fee for the player who enjoyed double joy last season, he won the Premier League title with Leicester and also won promotion to the Premier League when on loan at Middlesbrough.
The Belgian only made 12 appearances for the Foxes last season, but scored a vital goal against his new club Aston Villa.
He scored Leicester's first goal in a 3-2 victory over Villa, when the Foxes were trailing 2-0 and many say this match was the turning point for Leicester's success.