The Old Lady have chosen former Azzurri manager Spalletti to lead the team for the remainder of the campaign.
The experienced coach steps in for his predecessor, who was dismissed post the Lazio setback recently.
The former boss came on board in March to replace Thiago Motta but left after seven months after an eight-game winless streak.
Spalletti led Napoli to the Serie A title in 2022-23 prior to assuming the Italy role, which missed out on the 2022 World Cup under former boss Roberto Mancini.
He secured their spot in Euro 2024 exiting in the last 16 stage against 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.
Spalletti has also managed 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 for their 3-1 win against Udinese on Wednesday 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.
