The Old Lady have chosen former Italian national team boss the veteran manager to take the helm for the remainder of the campaign.
Spalletti takes over from his predecessor, who was let go after the Serie A side's defeat by Lazio last weekend.
Tudor had joined the club in March filling the shoes of Thiago Motta but left after seven months at the end of an eight-match winless run.
Spalletti led Napoli to the Serie A title in 2022-23 before taking charge of Italy, who had failed to qualify for the 2022 World Cup under former boss Roberto Mancini.
He helped them qualify for Euro 2024 but were eliminated in the round of 16 by Switzerland.
Nonetheless, Italy dismissed Spalletti in June following a loss to Norway in World Cup qualifying, with the Azzurri at risk of missing out on a third consecutive World Cup.
He has previously coached Inter Milan, Roma, and Udinese in Italy's top flight and secured two Russian Premier League titles with Zenit St Petersburg.
Massimo Brambilla took interim charge of Juventus for their 3-1 win against Udinese on Wednesday which left them seventh in Serie A - trailing leaders Napoli by six points after nine matches.
In the Champions League, they sit 25th in the league phase, having lost once and drawn twice in their opening three matches.
