Shiffrin finished 0.12 seconds ahead of Italy's Federica Brignone, with Norwegian Ragnhild Mowinckel rounding out the podium (+0.22).
The victory took Shiffrin to 13 career medals at the world championships: seven gold, three silver, three bronze. She has won at least one gold at every championships since 2013 and her 13 medals have come from just 16 career world championship races.
Shiffrin is now level with Anja Paerson on 13 world medals although the former Swede racer's haul includes two in the team event. Only Germany's Christl Cranz (15), skiing pre-WWII, has claimed more.
A seventh world title also saw Shiffrin draw level with Paerson, Marielle Goitschel, Marcel Hirscher and Toni Sailer, while Cranz has 12 to her name.
"When you take these big events, Olympics or world championships, everything boils down to one race," the 27-year-old said.
"The chances of it going really well are actually very small. Only three people can get a medal and only one person can win... It's a very rare thing to win a gold medal in any event."
That said, Shiffrin said she was skiing the best giant slalom of her life, highlighting her own "consistency and aggression".
"Today felt very special, it's a moment I'm going to remember forever."
High levels of stress
Shiffrin, who also bagged a world super-G silver last week on the same slope, came into the giant slalom after a turbulent few days that saw her dramatically split with long-time coach Mike Day.
"It was never the intention to make an official announcement during the world championships, but the ways things transpired that's how it happened," an emotional Shiffrin said, paying tribute to Day, who returned to the United States on Tuesday.
"It's been definitely some high levels of stress these days," she admitted, calling Day's departure "sad".
"It was very very difficult today to keep the focus and keep the intensity on the right level and the right direction to perform this way in this race."
Day, Shiffrin said, "has been such an integral part of my team, being there to support me through some of the most incredible moments of my career and some of the most challenging. He's been there to support me through it all".
Under Day's guidance since 2016 until Tuesday, Shiffrin is currently on the cusp of matching Swedish legend Ingemar Stenmark's World Cup record for overall victories (86), having already surpassed former teammate Lindsey Vonn's record for female victories (82) this season.
When Day took over as her head coach, she'd been on 20 World Cup victories. During his time as coach, she also bagged two of her three Olympic medals and 10 of her 13 world medals.
When asked whether she considered herself the greatest of all time, Shiffrin said that was for other people to decide.
"I don't think I can do anything to truly be the greatest of all time," she said.
"That's for people to decide on their own. Everybody gets to decide who their favourite athlete is. For many people that's not me and that's OK.
"I'm trying to push this sport, push the limits and share my passion for it with the world, hopefully bring fans to this sport.
"Some people will consider me the greatest and some people don't even consider me part of the conversation."
