The Serie A powerhouse have named ex- Italy manager Spalletti to lead the team for the remainder of the campaign.
The experienced coach replaces his predecessor, who was dismissed after the Serie A side's defeat by Lazio on Sunday.
Tudor had joined the club in March filling the shoes of Thiago Motta but exited following a seven-month stint after an eight-game winless streak.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 prior to assuming the Italy role, after the team's failure to reach the 2022 World Cup with Mancini at the helm.
Under his guidance, they made it to Euro 2024 where they were knocked out in the last 16 by Switzerland.
Yet, the Italian FA let Spalletti go in June following a loss to Norway in World Cup qualifying, 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 took interim charge of Juventus during the 3-1 victory over 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, with one loss and two draws in their first three games.
