The Old Lady have appointed former Azzurri head coach Spalletti to take the helm for the rest of the term.
Spalletti steps in for his predecessor, who was let go post the Lazio setback last weekend.
The former boss came on board 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 prior to assuming the Italy role, which missed out on the 2022 World Cup under former boss Roberto Mancini.
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 post a qualifying defeat against Norway, 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.
Massimo Brambilla took interim charge of Juventus during the 3-1 victory over Udinese on Wednesday placing them seventh in the Serie A standings - six points behind leaders Napoli after nine games.
Their Champions League campaign sees them in 25th place in the group stage, having lost once and drawn twice in their opening three matches.
