The Old Lady have named previous Azzurri boss Spalletti as their manager for the rest of the term.
The experienced coach replaces his predecessor, who was let go after the Serie A side's defeat by Lazio last weekend.
Tudor had joined the club in March to replace Thiago Motta 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 before taking charge of Italy, which missed out on the 2022 World Cup with Mancini at the helm.
He helped them qualify for Euro 2024 where they were knocked out in the last 16 by Switzerland.
However, Spalletti was sacked by Italy in June following a loss to Norway in World Cup qualifying, as Italy faced the possibility of not making a third World Cup in a row.
Spalletti's managerial career includes Inter Milan, Roma, and Udinese in Serie A and secured two Russian Premier League titles with Zenit St Petersburg.
Juventus were temporarily led by Massimo Brambilla for their 3-1 win against Udinese on Wednesday which left them seventh in Serie A - six points adrift of Napoli at the top after nine rounds.
Their Champions League campaign sees them in 25th place in the group stage, having lost once and drawn twice in their opening three matches.
