The Old Lady have chosen previous Italy manager Spalletti to take the helm for the remainder of the campaign.
The experienced coach takes over from his predecessor, who was let go following the loss to Lazio last weekend.
Tudor had joined the club in March as Thiago Motta's replacement but left after seven months after an eight-game winless streak.
Spalletti guided Napoli to the Serie A crown in 2022-23 prior to assuming the Italy role, after the team's failure to reach the 2022 World Cup during Roberto Mancini's tenure.
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 after a World Cup qualifying defeat by 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 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 adrift of Napoli at the top after nine rounds.
They are 25th in the league phase of the Champions League, having lost once and drawn twice in their opening three matches.
