Juventus have chosen former Azzurri boss the veteran manager to lead the team for the rest of the term.
The experienced coach replaces Igor Tudor, who was let go after the Serie A side's defeat by Lazio on Sunday.
Tudor arrived at the club in March to replace Thiago Motta but left after seven months after an eight-game winless streak.
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 under former boss Roberto Mancini.
Under his guidance, they made it to Euro 2024 but were eliminated in the round of 16 by Switzerland.
Yet, the Italian FA let Spalletti go in June post a qualifying defeat against Norway, as Italy faced the possibility of not making a third World Cup in a row.
He has previously coached Inter Milan, Roma, and Udinese in Italy's top flight and lifted the Russian league trophy twice while at Zenit St Petersburg.
Juventus were temporarily led by Massimo Brambilla during the 3-1 victory over Udinese on Wednesday placing them seventh in the Serie A standings - trailing leaders Napoli by six points after nine matches.
In the Champions League, they sit 25th in the league phase, with one loss and two draws in their first three games.
