"The choice of Didier Deschamps, whose playing and coaching career speaks for itself, was a natural one," a statement on Marseille's official website read.
"A meeting between the club’s president and its major shareholder last Friday confirmed this choice. After Eric Gerets, Marseille could only set their sights on a top coach."
Deschamps, 40, guided Monaco to the UEFA Champions League final in 2004, before leading Juventus back to Serie A three years later.
Belgian manager Gerets said earlier that he will leave Velodrome at the end of the season, despite his exploits with the team this term.
Marseille are in charge of the French league table but they face stern competition from joint-leaders Bordeaux, with four weeks to go.
Nonetheless, L'OM are on course to win their first trophy in 16 years and end Lyon's seven-year league domination in France.
Marseille's last trophy came in 1993, when they won the Champions League, with Deschamps captaining the team.