It was the 18th career World Cup victory for Ligety, who's hoping to challenge for the overall World Cup title this season after finishing third last year. Defending overall champion Marcel Hirscher of Austria was third on Sunday.
The 29-year-old Ligety is coming off a season in which he won three golds at the world championships, and he has been on the podium in nine straight World Cup giant slaloms.
Ligety endured changing conditions, from a sunny and slushy first run to a windy and bumpy second run, to clock a combined time of 1 minute, 59.50 seconds.
"Second run is always difficult," he said. "It's super dark on that pitch and it gets bumpy. There are a couple little tricky sections, so I'm glad I made it through. It wasn't clean but it was what I had to do to get the victory. It's a good day for sure. Any win is a good win and it's cool that I've been able to have this kind of success here in Soelden. It's always treated me well ever since my first time racing here, so it's definitely nice to get a win right off the bat."
Fellow American Bode Miller, the two-time overall World Cup champion, finished 19th in 2:02.79 in his first race in 20 months after recovering from a knee injury, while teammate Tim Jitloff finished 20th in 2:02.81.
"It was disappointing skiing today," Miller said. "It's not where I've been skiing the last weeks and obviously not where I want to start out. I didn't really come in with much of a goal. I wanted to obviously finish and see where I stacked up. I was hoping to ski similar to how I skied in training. That's always my goal. But you know, sometimes it doesn't happen."