The Old Lady have named former Azzurri head coach the veteran manager to take the helm until the end of the season.
Spalletti takes over from the Croatian manager, who was let go post the Lazio setback on Sunday.
Tudor arrived at the club in March as Thiago Motta's replacement but departed after seven months after an eight-game winless streak.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 then moving on to lead the Italian national team, who had failed to qualify for the 2022 World Cup under former boss Roberto Mancini.
He helped them qualify for 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, putting Italy in danger of missing a third straight World Cup.
He has previously coached Inter Milan, Roma, and Udinese in Italy's top flight and won the Russian Premier League twice with Zenit St Petersburg.
Massimo Brambilla took interim charge of Juventus for their 3-1 win against Udinese on Wednesday which left them seventh in Serie A - six points adrift of Napoli at the top after nine rounds.
In the Champions League, they sit 25th in the league phase, having lost once and drawn twice in their opening three matches.
