Juventus have named ex- Azzurri manager the veteran manager as their manager for the remainder of the campaign.
The 66-year-old 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 exited following a seven-month stint following a string of eight matches without a victory.
Spalletti led Napoli to the Serie A title in 2022-23 prior to assuming the Italy role, who had failed to qualify for the 2022 World Cup during Roberto Mancini's tenure.
Under his guidance, they made it to Euro 2024 but were eliminated in the round of 16 by Switzerland.
However, Spalletti was sacked by Italy in June post a qualifying defeat against Norway, as Italy faced the possibility of not making a third World Cup in a row.
Spalletti has also managed Inter Milan, Roma and Udinese in Serie A and won the Russian Premier League twice with Zenit St Petersburg.
Massimo Brambilla served as interim manager for Juventus during the 3-1 victory over Udinese on Wednesday which left them seventh in Serie A - six points behind leaders Napoli after nine games.
They are 25th in the league phase of the Champions League, after recording one defeat and two ties in the initial three fixtures.
