"Lazio announces that Maurizio Sarri has handed in his resignation as head coach of the first team," the club said in a statement on Wednesday.
"The club would like to thank the coach for his achievements and for the work he has done, wishing him the best of luck in his professional and personal life.
"At the same time, the club communicates that it has decided to entrust Giovanni Martusciello with the technical leadership."
Sarri had handed his resignation to the club's management on Tuesday, the Italian media reported.
Lazio, who on Monday suffered a 2-1 home defeat against Udinese, are ninth in the Serie A standings with 40 points from 28 games.
They lost five of their last six games across all competitions.
Former Chelsea and Napoli manager Sarri took over Lazio in June 2021 from Simone Inzaghi, who left to sign with Inter Milan.
The club last Thursday dismissed media reports saying Lazio considered sacking Sarri after their 3-0 defeat at Bayern Munich in the Champions League, the result that saw them out of the competition, stressing that his contract was expiring in 2025.
Martusciello was previously Sarri's assistant at Empoli and Juventus. He took over Empoli for his only previous head coach role in 2016-17 from Marco Giampaolo, after Sarri had left to coach Napoli.
Empoli were relegated on the final match day, seeing Martusciello part ways with the club. He was then appointed as technical coach at Inter Milan.
Martusciello will make his debut when Lazio travel to lowly Frosinone on Saturday.
