The OM captain and goalkeeper will leave the club at the end of the 2020-2021 season.
A three-year extension will allow, according to one Marseille, Mandanda “to rise even more to the legend. “
The 35-year-old, who will be 39 when his new contract expires, has played a record 549 games for OM.
Mandanda, signed from Le Havre in 2007, had a brief unsuccessful spell with Crystal Palace in the Premier League in 2016-17 before returning to Marseille.
France remained the starting goalkeeper for Marseille last season before the suspension of the Ligue 1 season due to the coronavirus pandemic.
His new crusade is expected to start late in Brest on Sunday after positive tests for COVID-19 led to the postponement of the first scheduled match.