The American slalom specialist and Olympic champion, who hopes for more gold at the Pyeongchang winter Games in February, blew past the competition to finish almost a second ahead of her nearest rival, second-placed and home favourite Tessa Worley.
Italian Manuela Moelgg was third just before talented Norwegian Ragnhild Mowinckel.
Goggia overcomes windy conditions to earn another downhill victory
Shiffrin, who skipped the World Cup event at Val D'Isere last week, had notched her first career World Cup win in downhill at Canada's Lake Louise earlier this month.
'This is Shiffrin at her best!' - American produces stunning second run to win in Courchevel
Germany's Viktoria Rebensburg, second overall, and top of the giant slalom standings going into the race after winning the two previous ones this season, paid the price for two sloppy runs to finish in 14th.
The Pyeongchang Olympics in South Korea run from Feb. 9-25.
Shiffrin shakes up coaching team ahead of Olympics with Lackie departure
Brignone top of the tree in Zauchensee Super G