The striker found the net for the 19th time this season to secure a point for the visitors after midfielder Antoine Devaux had put Reims midway through the second half.
Marseille enjoyed the better of the first half, with only a fine save from Kossi Agassa preventing Gignac from giving Jose Anigo's side the lead with a header.
Agassa was the busier of the two goalkeepers for much of the encounter and produced another excellent stop to deny Gignac again early in the second half.
Defender Rod Fanni then shot just over the bar from close range following an error from Agassa, before Steve Mandanda was called into action at the other end to keep out a Nicolas De Preville strike.
But Marseille were eventually made to pay for their profligacy as Devaux found the top corner with a fine header from Franck Signorino's cross.
However, Anigo's men responded well and levelled 10 minutes from time as Andre Ayew beat Agassa to a right-wing cross from Fanni, heading the ball back into the path of Gignac to slot into an empty net.
Both teams pressed for the winner in the closing stages, substitute Gaetan Courtet twice going close, but they were each left to settle for a point that does not help either team's European hopes.
Marseille are sixth, four points adrift of fourth-placed Saint-Etienne, while Reims are a point further back in seventh.
