Hirscher parlayed a sizzling first run of 56.69 seconds into a two-run combined time of 1 minute, 54.10 seconds and claimed the top step on the podium.
Stefan Luitz of Germany placed second with a 1:55.26 and Ted Ligety of the United States placed third.
Hirscher is the defending overall World Cup champion and also was the winner of the giant slalom title last season.
Ligety had his streak of giant slalom wins snapped at two; however his third place kept him atop the current point standings in the event and pulled him a little closer to Norway's Askel Lund Svindel in the overall points standings.
Ligety said third place was just fine with him considering the soft snow that prompted race officials to shorten Sunday's course. "Val d'Isere is always tough, it's not a hill I particularly like," he said. "It's very steep the whole way. I'm happy to salvage it and to walk away from this hill with a podium when it could easily have been a DNF (did not finish)."