Shiffrin kept her balance despite a big slide in the closing stages of her run and she crossed the finishing line 0.12 seconds ahead of Italy's Federica Brignone (32), in a total time of two minutes 7.13 seconds. Ragnhild Mowinckel (30) from Norway came in third.
"Today I really saw myself losing it ... I don’t even know how to explain it but my heart is going crazy, I feel like I am going to faint," a hugely relieved Shiffrin said.
"It’s unbelievable. I just thought I was going to lose it on the second run. I know how close it can be and I knew how hard I had to push and I didn’t know if I could do it."
The Alpine skier bagged her first giant slalom gold at the world championships. She had previously won four slalom world titles, one in super-G and one in combined.
Shiffrin has now struck gold at each of the last six world championships, with an overall tally of 13 medals at the event.
Shiffrin could increase her tally on Saturday when she competes in the slalom.
