The Serie A powerhouse have chosen former Azzurri manager Spalletti to lead the team until the end of the season.
The experienced coach steps in for his predecessor, who was let go post the Lazio setback on Sunday.
Tudor had joined the club in March to replace Thiago Motta but left after seven months after an eight-game winless streak.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 then moving on to lead the Italian national team, which missed out on 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.
However, Spalletti was sacked by Italy in June after a World Cup qualifying defeat by Norway, with the Azzurri at risk of missing out on a third consecutive 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 served as interim manager for Juventus in the midweek 3-1 triumph over Udinese placing them seventh in the Serie A standings - six points behind leaders Napoli after nine games.
Their Champions League campaign sees them in 25th place in the group stage, having lost once and drawn twice in their opening three matches.
Elena is a freelance writer and mindfulness coach who loves exploring the power of positive thinking.