In the summer of 2015, Rugani officially returned to Juventus. He made his debut with the club on 30 September 2015, coming on as a substitute in a 2–0 home win over Sevilla in the UEFA Champions League group stage, also making his European debut in the process. He made his first start with the club on 16 December, in a 4–0 win over cross-city rivals Torino in the "Derby della Mole" in the round of 16 of the Coppa Italia. His league debut with the club came four days later, as he came on for veteran defender Andrea Barzagli in the 56th minute of a 3–2 away win over Carpi. He made his first league start for the club in a 2–1 away win over Sampdoria in Serie A, on 10 January 2016. On 24 April, Rugani was booked for the first time in his entire Serie A career in his 53rd Serie A appearance. He received a yellow card in the 72nd minute of a 2–1 away win over Fiorentina; he had last been carded at club level with Empoli, on 1 March 2014, in an away Serie B fixture against Siena. Following Napoli's loss to Roma the following day, Juventus clinched the league title with three games to spare.