Lazio will unveil the French player at a press conference in Rome at 6pm (GMT) tonight after Saha was released by Sunderland during the January transfer window.
Saha, now 34, failed to score in 11 appearances for Sunderland, and has enjoyed limited success since departing Manchester United for Everton in 2008.
He netted 27 times in 97 appearances at Goodison Park over a four-year period before hitting four goals in 11 outings for Tottenham last term.
Saha said on Twitter: "In Paris, now for Rome. Good morning."
Lazio are looking for cover with German striker Miroslav Klose missing for two months due to a knee injury.