Five-star Shiffrin crowned overall ski World Cup champion
The 27-year-old finished fifth but crucially ahead of her only rival for the crown, Swiss racer Lara Gut-Behrami, in the women's downhill at Kvitfjell.
With 700 points still available, two-time Olympic gold medallist Shiffrin holds a 796-point lead.
Shiffrin has dominated the season, posting 14 podium finishes, including 11 victories, in 25 races.
"For me it's quite special to have it now already," she said. "And I can take a little bit of weight off my shoulders.
"In the middle of the season I was always thinking 'oh, I just have to keep pushing because it's not done yet'. And so now at least that's done and I can enjoy myself more."
The American's tally of five overall titles equals Luxembourg's Marc Girardelli. Just two Austrians, Annemarie Moeser-Proll, who won six overall titles, and eight-time winner Marcel Hirscher are ahead of her.
An even bigger prize awaits Shiffrin as she could round the weekend off by equalling Swedish ski icon Ingemar Stenmark's World Cup record of 86 victories.
She races in the super-G on Sunday before heading to Stenmark's homeland to compete in the giant slalom and slalom next weekend in Are.
Shiffrin will be presented with the Crystal Globe at the World Cup finals in Andorra on March 19.
Saturday's downhill was won by 24-year-old Kajsa Vickhoff Lie, which was a first in World Cup history for a female Norwegian skier.
Sofia Goggia's second placed finish was sufficient for the Italian to be assured of winning that discipline's title.