The Serie A powerhouse have named ex- Azzurri head coach the veteran manager as their manager for the rest of the term.
Spalletti steps in for his predecessor, who was sacked post the Lazio setback on Sunday.
Tudor arrived at the club in March to replace Thiago Motta but left 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, which missed out on the 2022 World Cup with Mancini at the helm.
Under his guidance, they made it to Euro 2024 exiting in the last 16 stage against Switzerland.
However, Spalletti was sacked by Italy in June after a World Cup qualifying defeat by Norway, with the Azzurri at risk of missing out on a third consecutive World Cup.
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 in the midweek 3-1 triumph over Udinese placing them seventh in the Serie A standings - six points adrift of Napoli at the top after nine rounds.
They are 25th in the league phase of the Champions League, after recording one defeat and two ties in the initial three fixtures.
