After winning the U.S.' first Olympic title along with now-retired Kikkan Randal at PyeongChang 2018, the Minnesota-born skier has become the first American to clinch the World Cup overall title 39 years after Olympic silver medallist Bill Koch.
Diggins is also the first American woman to win cross country skiiing's biggest prize.
With just two races left in the calendar (a 10km and 30km pursuit in Engandin, Switzerland), the American tops the rankings with 1,246 points, 342 ahead of second-placed Yulia Stupak from Russia.
Since just 200 points will be at stake and after the cancellations of the event in Oslo and the World Cup Finals (re-scheduled from Beijing to Lillehammer and then cancelled completely), Diggins can celebrate her historic achievement without even competing.
Diggins recently also became the first non European to claim the Tour de Ski.
Diggins finished overall runner-up in the 2017-18 season and during this campaign she's been the most consistent skier claiming four races and nine podiums in total.
The Olympic champion, who ended the recent World Ski championships in Oberstdorf with two fourth places, succeeds to last year's winner Therese Johaug, becoming the first woman outside of Norway to win the title since four-time champion Justyna Kowalczyk of Poland in 2013.