The four-time world champion clocked 2:35.77 to finish just ahead of American team-mate Bode Miller while Austria's Marcel Hirscher claimed third.
It was Ligety's 10th consecutive giant slalom podium and Miller's first in the discipline in six years.
Ligety's win was set up by a blistering first run that gave him a 1.26-second advantage over the field, and he credited his unusual approach to giant slalom, which involves taking a longer line but one that allows him to accelerate out of corners more effectively.
"I ski a turn far differently than most guys," Ligety said.
"If you compare myself to my biggest competitor, Marcel Hirscher, he skis in kind of a jumpy manner. He skips the top 10 percent of his turn and lands on a clean edge, but he doesn't take the turn quite as deep, which gives the advantage of being more precise but isn't as fast, doesn't get as much rebound out of the turn.
"There's a little bit of a give-and-take with that. I take the turn a lot deeper and cleaner and rounder. That gives me more rebound, especially on the new skis, to generate speed. Also I'm decelerating less, because I'm not hitting the skis hard in one spot.
"On the old skis, skipping the top 10 percent of the turn, you could get just as much rebound as arcing it fully.
"I have been working on the way I've been skiing since 2005 or so, trying to really take the turn deep and ski differently than everybody else. I thought that was the way to really separate myself."