Hosts Germany completed the two-week event without a gold medal after their big hope Felix Neureuther straddled a gate in the second of the two runs.
Grange, 26, bronze medallist in Are four years ago, emulated compatriot Jean-Noel Augert, the last Frenchman to win the title in 1970 in Val Gardena.
Grange’s win came after two years of frustration which saw him crash out of contention on home snow in Val d’Isere two years ago before missing the Vancouver Olympics with a knee injury.
Fastest in the first leg, the 2009 slalom World Cup winner held his nerve to win in a combined time of one minute and 41.72 seconds.
“It was hard to handle the wait between the two runs. It was horribly long. My demons from 2009 were coming back in my mind. But I had trust in myself and I did the job,” Grange told reporters.
“I’m enormously happy to have made it and to emulate Augert, who comes from the same valley as me.”
The victory, ending a run of three successive world titles for Austria in the event, crowned an excellent world championships for France with two gold medals, one silver and a bronze.
Sweden’s Jens Byggmark took the silver medal 0.43 seconds adrift while Italy’s Manfred Moelgg, a silver-medallist in Are in 2007, was third.
Veteran Austrian Mario Matt, the slalom world champion in 2001 and 2007, narrowly missed the podium, finishing fourth.
His compatriot Manfred Pranger, the defending champion, was a disappointing ninth, just behind pre-race favorite Ivica Kostelic who was obviously ill at ease on the rugged Gudiberg course.
Kostelic has already made it clear that his priority this season is to win the overall World Cup, in which he holds a commanding lead.
He missed part of the world championships, returning him to rest by the Adriatic sea.
