Marrone, who had been linked with moves to La Liga's Sevilla and Everton in the Premier League, has joined the newly promoted Serie A side on a co-ownership deal.
The 23-year-old has been capped 30 times by Italy Under-21s, but only managed to make 18 appearances in the previous two seasons for Antonio COnte's side as they marched to consecutive Serie A titles.
He will now link up with his new team-mates at Stadio Citta del Tricolore, with Sassuolo bottom of the league after just two games in the Italian top flight.
Juventus have done further business by signing Berardi frm the same club, also on a co-ownership deal.
The 19-year-old scored 11 goals in 37 games last season as Sassuolo earned promotion from Serie B, but is yet to feature in the top flight due to suspension.
Berardi will have to wait a while for his Juve debut, as he will spend the rest of the season on loan back at Sassuolo.
