The Chilean has brought an end to a near 12-month absence from the game as he takes charge of the ninth club of his coaching career
Jose Anigo has been the club's interim boss since the December departure of Elie Baup, but OM have opted not to hand the 53-year-old the position on a permanent basis.
Bielsa has earned a reputation as an attacking and innovative coach during a 24-year managerial career that has taken in spells in charge of Argentina, Chile and Athletic Bilbao in recent years.
The 58-year-old departed Bilbao at the end of his contract in June 2013 and turned down the chance to manage Paraguay before ending his near 12-month absence from the game on Friday.
Marseille's president Labrune Vincent said: "I can tell you that our lawyers and those of Marcelo Bielsa have reached a legal and contractual agreement which makes Marcelo Bielsa the next coach of Olympique de Marseille for the next two seasons."
OM are currently sixth in Ligue 1 having finished runners-up to reigning champions Paris Saint-Germain last term. The club last lifted the league title in 2010.