The Old Lady have appointed former Azzurri manager the veteran manager as their manager for the remainder of the campaign.
Spalletti steps in for the Croatian manager, who was sacked post the Lazio setback recently.
The former boss came on board in March filling the shoes of Thiago Motta but left after seven months at the end of an eight-match winless run.
Spalletti led Napoli to the Serie A title in 2022-23 then moving on to lead the Italian national team, after the team's failure to reach the 2022 World Cup with Mancini at the helm.
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, 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.
Massimo Brambilla served as interim manager for Juventus in the midweek 3-1 triumph over Udinese placing them seventh in the Serie A standings - trailing leaders Napoli by six points after nine matches.
They are 25th in the league phase of the Champions League, after recording one defeat and two ties in the initial three fixtures.
