Juventus have named former Azzurri head coach the veteran manager to lead the team until the end of the season.
The 66-year-old takes over from Igor Tudor, who was sacked following the loss to Lazio last weekend.
Tudor arrived at the club in March as Thiago Motta's replacement but left after seven months at the end of an eight-match winless run.
Spalletti guided Napoli to the Serie A crown in 2022-23 before taking charge of Italy, who had failed to qualify for the 2022 World Cup with Mancini at the helm.
Under his guidance, they made it to Euro 2024 where they were knocked out in the last 16 by Switzerland.
Nonetheless, Italy dismissed Spalletti in June post a qualifying defeat against Norway, putting Italy in danger of missing a third straight World Cup.
Spalletti's managerial career includes Inter Milan, Roma, and Udinese in Serie A and secured two Russian Premier League titles with Zenit St Petersburg.
Juventus were temporarily led by Massimo Brambilla in the midweek 3-1 triumph over Udinese placing them seventh in the Serie A standings - six points adrift of Napoli at the top after nine rounds.
They are 25th in the league phase of the Champions League, having lost once and drawn twice in their opening three matches.
