The Old Lady have named ex- Azzurri head coach the veteran manager as their manager for the rest of the term.
The 66-year-old replaces the Croatian manager, who was dismissed following the loss to Lazio last weekend.
Tudor arrived at the club in March as Thiago Motta's replacement but exited following a seven-month stint at the end of an eight-match winless run.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 before taking charge of Italy, which missed out on the 2022 World Cup under former boss Roberto Mancini.
He secured their spot in 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.
Spalletti's managerial career includes Inter Milan, Roma, and Udinese in Serie A and won the Russian Premier League twice with Zenit St Petersburg.
Juventus were temporarily led by Massimo Brambilla in the midweek 3-1 triumph over Udinese placing them seventh in the Serie A standings - six points behind leaders Napoli after nine games.
In the Champions League, they sit 25th in the league phase, having lost once and drawn twice in their opening three matches.
