The Old Lady have appointed former Italy boss the veteran manager to lead the team for the rest of the term.
Spalletti replaces the Croatian manager, who was dismissed following the loss to Lazio last weekend.
Tudor had joined the club in March to replace Thiago Motta but left after seven months following a string of eight matches without a victory.
Under Spalletti, Napoli clinched the Serie A championship in 2022-23 before taking charge of Italy, 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.
However, Spalletti was sacked by Italy in June after a World Cup qualifying defeat by 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 lifted the Russian league trophy twice while at 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 - trailing leaders Napoli by six points after nine matches.
In the Champions League, they sit 25th in the league phase, after recording one defeat and two ties in the initial three fixtures.
