Garcia will take charge for the French giant's clash against arch-rivals Paris Saint-Germain on Sunday.
Garcia replaces Franck Passi and will take charge for the French giant's clash against arch-rivals Paris Saint-Germain at the Parc des Princes on Sunday.
"Rudi Garcia, 52, has signed a three-year contract. He will take up his role" starting Friday, Marseille said in a statement.
The appointment comes just three days after US tycoon Frank McCourt completed his purchase of the Ligue 1 side from Margarita Louis-Dreyfus.
"When I met Rudi, he told me straight away he wanted to win the Champions League," said McCourt, who has vowed to restore Marseille to their former glory.
"I immediately knew he would be the man for the job," added the Boston-born former owner of the Los Angeles Dodgers.
Garcia guided Lille to a league and French Cup double in 2011 and was last in charge of Roma before he was sacked in January, having steered the Serie A side to successive second-place finishes behind Juventus.
Roma earlier confirmed they had terminated Garcia's contract by mutual agreement, with the Frenchman still having been tied to the Italian club.