The 22-year-old American scored a third place in a giant slalom in Germany to take an unassailable lead in the season standings ahead of next week's World Cup finals in Are, Sweden.
Shiffrin becomes the fourth woman this century to retain the overall crown after Sweden's Anja Paerson, American Lindsey Vonn and Austria's Anna Veith (nee Fenninger).
The Olympic giant slalom champion took her season points tally to 1573 with her only rival, Austria's Wendy Holdener, second on 970. With six races left this season and 100 points available for a win, Shiffrin's total can't be passed.
She is also likely to clinch a fifth straight slalom World Cup crown with two races left.
Austria's Annemarie Moser-Proell holds the women's record with six overall titles between 1969 and 1980. Vonn, who won three in a row from 2008-2010, is second with four.
Shiffrin went to the Winter Olympics in Pyeongchang with a realistic chance of winning multiple gold medals but after triumphing in the giant slalom she faltered in the defence of her slalom title from Sochi, finishing fourth.
She hit back with a silver in the combined but the knock-on effects of a compressed schedule because of bad weather meant she declined to race the downhill or super-G, putting paid to pre-Games talk of possible golds in all five of skiing's individual disciplines.
"I don't know if that's possible," Shiffrin told CNN in South Korea. "It's a really difficult thing to do, that's for sure.
"Let's say that everything here worked out perfectly, the schedule went off without a hitch, no wind, none of that, those kinds of factors, I think the most I could have walked away from this Olympics was three medals, not necessarily all gold."
Shiffrin, the three-time slalom world champion, set the World Cup circuit abuzz when she clinched her first ever downhill victory in December in only her fourth ever speed race.
She won 10 races across four disciplines, with six other podium places, to secure the overall crown but admitted an Olympic cleansweep was only a "dream."
"I was not at the level, with either downhill or super-G, to be a real medal threat, even given my results this season and last season in speed events," she added in Pyeongchang.
"It was nice to dream about, but it wasn't there.
"So, to have two medals, for me, that's a huge success, especially with the weather conditions."