Juventus have named ex- Italian national team manager the veteran manager to take the helm until the end of the season.
The 66-year-old takes over from his predecessor, who was let go following the loss to Lazio last weekend.
The former boss came on board in March as Thiago Motta's replacement but exited following a seven-month stint at the end of an eight-match winless run.
Spalletti guided Napoli to the Serie A crown in 2022-23 prior to assuming the Italy role, who had failed to qualify for the 2022 World Cup under former boss Roberto Mancini.
Under his guidance, they made it to Euro 2024 where they were knocked out in the last 16 by Switzerland.
However, Spalletti was sacked by Italy in June after a World Cup qualifying defeat by Norway, as Italy faced the possibility of not making a third World Cup in a row.
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 which left them seventh in Serie A - six points behind leaders Napoli after nine games.
In the Champions League, they sit 25th in the league phase, having lost once and drawn twice in their opening three matches.
