France stay four points behind Group Seven leaders Serbia, who thumped Romania 5-0, and will finish second to face a playoff whatever the outcome of their last group game against Austria on Wednesday in Paris.
Gignac opened the scoring from close range on 34 minutes and doubled the advantage with a superb angled shot from just inside the box five minutes later.
Defender William Gallas made it 3-0 with a headed goal early in the second half before striker Nicolas Anelka and substitute forward Karim Benzema wrapped it up with late efforts.
France have 18 points from nine games, four more than third-placed Austria, who beat Lithuania 2-1, and are certain to finish among the eight best second-placed teams who will face two-legged playoffs next month.
"You couldn't ask for much more," France coach Raymond Domenech told reporters after a convincing performance from the former world and European champions.
France, the World Cup runners-up in 2006, had been booed by their own fans in previous outings but the atmosphere was good on Saturday.
"The team showed that it deserved to be supported," Domenech added. "There is quality in that team and we will need to confirm that in a month.
"It's never easy to qualify and whatever opponents we face the playoff will be tough but this team is growing and showing it has style."
The home side dominated throughout the match, creating a string of chances and hitting the woodwork twice before opening the scoring.
Polish referee Robert Malek had to be replaced by fourth official Pawel Gil because of a calf muscle injury with 13 minutes left.
A minute's silence was held before the game in this small Brittany town in memory of Brice Taton, the Toulouse fan who died last week after being attacked by Partizan Belgrade fans before a Europa League game in the Serbian capital on September 17.
