Details of the deal were not disclosed by the club, but Italian news agency Adnkronos reported that the former Chelsea and Juventus manager Sarri has rejoined Lazio on a two-year contract with an option for a third season.
Sarri resigned as Lazio coach in March 2024, almost three years into his tenure. They finished seventh in Serie A in 2023-24, having finished second the previous season.
"Maurizio Sarri has returned home. His return is a choice of heart, conviction and vision," club president Claudio Lotito said in a statement.
"With him, we want to resume a path interrupted too soon, aware that together we can bring back enthusiasm, identity and ambition. Welcome back to your home, Commander."
Lazio finished seventh this season under Marco Baroni.