The 25-year-old midfielder spent last season on loan at Serie B team Modena, scoring three goals in 41 games.
However, he will now head to the second tier in England with Leeds, who are facing their 11th successive season outside of the Premier League.
Bianchi made over 60 appearances for Sassuolo, finding the net on just four occasions.
He previously spent six years with Piacenza having come through the ranks, playing 81 times.
Leeds have already signed goalkeepers Marco Silvestri and Stuart Taylor this close season.
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