The Austrian, 27, took gold after a sensational second run which gave him a combined time of 2:13.31 after a delay caused by a Swiss air force plane slicing through an overhead television camera cable.
The incident during an air display before the second run sent the camera crashing to the snow in the finish area, without hitting anyone, and led to a 30-minute delay due to the chairlift being halted for safety reasons.
The plane landed safely at a nearby airport.
Hirscher, who led team mate Roland Leitinger to an Austrian one-two with Norway’s Leif Kristian Haugen taking the bronze, has had previous experience of objects falling out of the sky during a ski race
In 2015 he criticized the use of drones to film races after one of them crashed and almost hit him while he was competing at Madonna di Campiglio in the Italian Alps.
Friday’s victory ended his long wait for a first giant slalom gold after the five times overall World Cup champion took silver in 2013 and 2015. The gold was his fifth at a world championships, and third in an individual event.
Hirscher completed his run in 1:06:73 ahead of fellow-Austrian Phillipp Schoerghofer, who came in at 1:06.99.
It was a good start for Hirscher, who was hoping for his first career gold at the event, having left with silver medals in the last two World Championships.
Frenchman Alexis Pinturault finished with a gap of +0.35 in 1:07.08, with Swede Matts Olsson just behind in 1:07.12.
Carlo Janka, who took the gold in 2009, finished the first round in 16th place in 1:08.05.
Speaking in an interview on the podium after the event Hirscher was very grateful and labelled the race one of the toughest of the season.
“It’s an unbelievable feeling after one of the toughest races we’ve had this season so far,
“I am very thankful for this.
“The GS was the gold medal that I had yet to win so today’s race had great meaning for me.”
Giant Slalom overall results
1. Marcel Hirscher (Austria) 1:06.73 1:06.58 2:13.31
2. Roland Leitinger (Austria) 1:07.26 1:06.30 2:13.56
3. Leif Kristian Haugen (Norway) 1:07.27 1:06.75 2:14.02
4. Henrik Kristoffersen (Norway) 1:07.21 1:06.86 2:14.07
5. Philipp Schoerghofer (Austria) 1:06.99 1:07.17 2:14.16
6. Matts Olsson (Sweden) 1:07.12 1:07.12 2:14.24
7. Alexis Pinturault (France) 1:07.08 1:07.21 2:14.29
8. Justin Murisier (Switzerland) 1:07.84 1:06.46 2:14.30
9. Mathieu Faivre (France) 1:07.51 1:06.85 2:14.36
10. Riccardo Tonetti (Italy) 1:07.58 1:06.89 2:14.47