The 24-year-old world champion finished ahead of Sweden's Jessica Lindell-Vikarby while Slovenian Tina Maze was third.
It was a first win for a French skier this season so far and came as something of a surprise as she had been struggling for form.
But 24-year-old Worley enjoys competing at Saint Moritz having taken a place on the podium in the three World Cup giant slaloms — including a win in the 2010/11 season — she has competed in.
It was her first World Cup win since the giant slalom at Soldeu in Andorra in February 2012, although she did win the world title this year.
Lindell-Vikarby's second place ensured she retained the overall lead in the giant slalom standings, having won at Beaver Creek in the season opener.
Switzerland's Lara Gut failed to finish in front of a home crowd of supporters but retained the lead in the overall World Cup standings
For reigning overall World Cup champion Maze it was a welcome return to form after a poor start to the season previously bereft of any podium finishes.