The 20-year-old striker will spend the coming season at Bologna on loan, while the Australian midfielder moves to the Azzurri d'Italia in a co-ownership deal
The Italian champions have secured half of the the young striker's economic rights, but immediately decided to farm him out on loan to Bologna for the coming season.
Gabbiadini, 20, scored once in 23 appearances for the Orobici last term and marked the start of the new campaign with his maiden cap for Italy in the 2-1 friendly defeat to England.
Meanwhile, Australia international Troisi has finalised his move to Juventus from Turkish side Kayserispor but will ply his trade with Atalanta next season.
The winger successfully underwent a medical with the Bianconeri on Thursday, and forms part of the agreement involving Gabbiadini's switch to Turin.
The pair join the likes of Lucio, Sebastian Giovinco, Kwadwo Asamoah and Mauricio Isla in signing on at Juventus Stadium this summer.