The Serie A powerhouse have appointed ex- Italian national team manager Spalletti to lead the team for the rest of the term.
The experienced coach replaces his predecessor, who was dismissed after the Serie A side's defeat by Lazio last weekend.
Tudor had joined the club in March as Thiago Motta's replacement 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, who had failed to qualify for the 2022 World Cup under former boss Roberto Mancini.
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 has also managed Inter Milan, Roma and Udinese in Serie A and lifted the Russian league trophy twice while at Zenit St Petersburg.
Massimo Brambilla took interim charge of Juventus for their 3-1 win against Udinese on Wednesday 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.
