Having already won the super-G and super combined events, a hat-trick was always on the cards for the American in his favourite event, although he had to survive a couple of slips on the second run before winning by 0.81 seconds.
Ligety, who has not failed to complete a giant slalom race for four years and totally dominates the event, led by one-and-a-half seconds after the first run, although his time on the second was only sixth best.
Austrian favourite Marcel Hirscher, who leads the season's overall standings on the World Cup circuit which he won last year, was second after overcoming a back injury to produce a storming second run which brought the home crowd to its feet.
Italy's Manfred Moelgg was third.
"It may have looked easy but I can say I had to fight hard in both runs," Ligety, combined gold medallist at the 2006 Olympics, said at the finishing line.
"The course was incredibly bumpy... it was a struggle from top to bottom."
The 28-year-old said that his previous wins were bonuses but his priority had been to win another gold in his favourite event.
"The main goal was to come here to defend my title," said Ligety, whose 15 wins on the World Cup circuit have all come in the giant slalom.
Hirscher, who has never won an individual gold in the World Championships, said he had a sleepless night after undergoing treatment on his back and suffering with a headache.
"I had only had five hours sleep and needed a lot of therapy on my back and neck, and it was still a bit painful," said Hirscher, who has Saturday's slalom still to look forward to.
"It's superb just to get this silver medal, the crowd was amazing. I heard the roar and this was the most exciting moment in my career."
Ligety joined the illustrious company of Austrian Toni Sailer, Frenchmen Jean-Claude Killy and Emile Allais and Norwegian Stein Eriksen, the only other men to have won three or more golds at the World Championships.
There is some debate about whether the tallies can be fairly compared, however, as the super combined and super-G events have only existed since the 1980s, making it easier to obtain a three-medal haul.
Ligety has won four of the five giant slalom races on the World Cup circuit this season and finished on the podium in the other.
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- Marcel Hirscher