The Old Lady have named ex- Azzurri head coach the veteran manager as their manager for the rest of the term.
The experienced coach steps in for the Croatian manager, who was dismissed after the Serie A side's defeat by Lazio on Sunday.
Tudor arrived at the club in March filling the shoes of Thiago Motta but left after seven months following a string of eight matches without a victory.
Spalletti guided Napoli to the Serie A crown in 2022-23 prior to assuming the Italy role, which missed out on the 2022 World Cup during Roberto Mancini's tenure.
He secured their spot in Euro 2024 but were eliminated in the round of 16 by Switzerland.
Nonetheless, Italy dismissed Spalletti 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 won the Russian Premier League twice with Zenit St Petersburg.
Massimo Brambilla took interim charge of Juventus during the 3-1 victory over Udinese on Wednesday placing them seventh in the Serie A standings - trailing leaders Napoli by six points after nine matches.
Their Champions League campaign sees them in 25th place in the group stage, with one loss and two draws in their first three games.
