The 25-year-old has signed a three-year contract at Elland Road, becoming the club's third signing of the summer following the arrivals of goalkeeper's Stuart Taylor and Marco Silvestri.
After helping Sassuolo to promotion to Serie A in 2013, Bianchi spent last season back in Serie B on loan at Modena, where he made 41 appearances and scored three goals.
He is expected to make his debut in a white shirt in tomorrow's pre-season friendly against Viitorul Constanta.