Barton joined on loan from Queens Park Rangers but had to serve a 12-match suspension that was extended to the French league.
"Really looking forward to making my league debut for Marseille on Sunday," Barton wrote on his Twitter account.
"Feel fitter and stronger than ever before. Cannot wait to pay back the fans and the club for showing me love during this turbulent period."
The 30-year-old was suspended by the English FA after being sent off for violent conduct in QPR's final Premier League match of last season against Manchester City.
"It's an image that crossed the Channel and that he carries with him," Marseille boss Elie Baup told reporters on Friday.
"He is a player with a character."
"He is a very different guy compared to the image that has been pinned to him," the Cameroon defender said.
"On and off the pitch, the image of the guy who throws punches and does absolute nonsense is completely false."
