The Italian, who has previously coached Valencia, Napoli and AC Milan, was hired by Marseille as Marcelino's replacement in September last year.
Marseille are ninth in the French top flight after a winless run of five league matches, out of which they have lost two and drawn three.
"Olympique de Marseille announces the end of its collaboration with Gennaro Gattuso," Marseille said in a statement.
"Marseille would like to extend its special thanks to Gennaro and his entire staff for the unfailing commitment and professionalism they have shown on a daily basis, and wishes them all the best for the future."
Gasset most recently coached the Ivory Coast national team. He was sacked after a poor performance in the group stage of the Africa Cup of Nations, which they scraped through as the last lucky loser. Ivory Coast went on to win the tournament.
Gasset most recently coached the Ivory Coast. He was sacked after the team's poor performances in the Africa Cup of Nations group stage, which they scraped through as the last lucky loser before going on to win the tournament.
"It's a huge honour for me to be joining this legendary club, Olympique de Marseille. I can't wait to start working with this group to prepare for the upcoming fixtures and give the best of ourselves," Gasset said.
Marseille did not give any details on Gasset's contract.
Marseille, on 30 points from 22 matches, next host Ukrainian side Shakhtar Donetsk in the Europa League knockout play-off second leg on Thursday, followed by another home game against 14th-placed Montpellier in Ligue 1 on Sunday.
