The youngster joins Villa in a summer of drastic change, with several top stars departing following last season's Europa League win.
Mbaye is Unai Emery's 10th summer signing and joins the likes of Johan Manzambi, Nicolas Jackson, Zion Suzuki and Leon Goretzka - among others.
His arrival represents a bit of a coup for Villa, with Mbaye grabbing four goals and four assists in his breakout campaign and earning a call-up to Senegal's 2026 World Cup squad.
The winger was in attendance for Villa's narrow 1-0 defeat to Premier League champions Arsenal on Monday evening.