The Serie A powerhouse have named ex- Italy boss the veteran manager as their manager for the rest of the term.
The experienced coach steps in for his predecessor, who was dismissed after the Serie A side's defeat by Lazio last weekend.
Tudor had joined the club in March as Thiago Motta's replacement but left after seven months at the end of an eight-match winless run.
Spalletti guided Napoli to the Serie A crown in 2022-23 then moving on to lead the Italian national team, after the team's failure to reach the 2022 World Cup under former boss Roberto Mancini.
He helped them qualify for Euro 2024 exiting in the last 16 stage against Switzerland.
However, Spalletti was sacked by Italy 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 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 which left them seventh in Serie A - trailing leaders Napoli by six points after nine matches.
Their Champions League campaign sees them in 25th place in the group stage, after recording one defeat and two ties in the initial three fixtures.
