Juventus have appointed previous Azzurri manager the veteran manager to lead the team until the end of the season.
The 66-year-old takes over from Igor Tudor, who was sacked post the Lazio setback on Sunday.
Tudor had joined the club in March as Thiago Motta's replacement but left after seven months following a string of eight matches without a victory.
Spalletti led Napoli to the Serie A title 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 secured their spot in Euro 2024 exiting in the last 16 stage against Switzerland.
However, Spalletti was sacked by Italy in June after a World Cup qualifying defeat by Norway, 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 won the Russian Premier League twice with Zenit St Petersburg.
Massimo Brambilla took interim charge of Juventus in the midweek 3-1 triumph over Udinese moving them to seventh position in the league - six points adrift of Napoli at the top after nine rounds.
They are 25th in the league phase of the Champions League, after recording one defeat and two ties in the initial three fixtures.
