Hirscher made it two victories in succession for the alpine giants when he held on to his advantage from the first run.
A day after compatriot Max Franz secured his maiden World Cup win in a downhill, Hirscher made it two victories in succession for the alpine giants when he held on to his advantage from the first run to triumph in the Italian Dolomites.
It was the fourth time in a row the Austrian, who has claimed the overall title each of the last five years, has won the giant slalom at the Italian resort.
France's Mathieu Faivre came second after countryman Alexis Pinturault, a key rival of Hirscher, crashed out in the second run.
In what was his 100th World Cup race, Italian Florian Eisath finished third to step on to the podium for the first time -- 12 years after making his debut.
It is Hirscher's second win of the season after a slalom victory in Levi, Finland, but his first in the giant this campaign after finishing runner-up twice earlier this month at Val d'Isere, France.
Having finished second to both Faivre and Pinturault at Val d'Isere in recent weeks, Hirscher admitted he has been working hard to reach the benchmark they have set.
"I'm super happy with my first victory of the season in GS (giant slalom) so far," said Hirscher.
"I've been on the podium the last three races and although it's good to get the points I haven't been perfect all the time, so I was thinking I have to get better.
"We've worked pretty hard in the past couple of weeks to get closer to the French team. They're the benchmark at the moment."
Hirscher's consistency this season has allowed the Austrian to tighten his grip at the top of the overall World Cup standings.
He has a tally of 540 points -- 340 of which have come from giant slalom races alone.
Norway's Kjetil Jansrud is second overall on 322 with Pinturault third on 284.
The men's World Cup continues at Alta Badia with a parallel giant slalom on Monday.