The Serie A powerhouse have appointed ex- Italian national team manager the veteran manager as their manager for the rest of the term.
The experienced coach steps in for his predecessor, who was sacked following the loss to Lazio last weekend.
Tudor arrived at the club in March to replace Thiago Motta but departed after seven months following a string of eight matches without a victory.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 then moving on to lead the Italian national team, which missed out on 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 following a loss to Norway in World Cup qualifying, putting Italy in danger of missing a third straight World Cup.
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 took interim charge of Juventus during the 3-1 victory over Udinese on Wednesday which left them seventh in Serie A - trailing leaders Napoli by six points after nine matches.
Their Champions League campaign sees them in 25th place in the group stage, after recording one defeat and two ties in the initial three fixtures.
