The 27-year-old from Calgary and the 25-year-old Valois, of Zenon, Park, Sask., blazed a half-second lead into the fourth and final run down the track, beating the field by nearly seven-tenths of a second with a combined four-run time of four minutes, 30.31 seconds.
"I'm ecstatic," Humphries said in a release. "Our goal all year was to win world championships and we did it. This is the perfect end to a great season and to do it in St. Moritz is the ultimate for any bobsledder.
"People don’t understand what this place means to us athletes. It is the birthplace of our sport and the longest track in the world that demands experience and skill so it means the world to me to win the world championships here."
Americans Elana Meyers and Katie Eberling claimed silver with a time of 4:30.99, while Germany's Sandra Kiriasis and Franziska Bertels earned bronze at 4:31.01.
Edmonton's Jenny Ciochetti drove the Canada 2 sled to 18th place with Calgary's Kate O'Brien. The Canadians raced to a 4:35.14 in their first worlds appearance together.
Humphries, the reigning Olympic champion, has 10 victories in her last 12 international races dating back nearly one year to the day. She won a silver medal last week in Igls, Austria, missing gold by .01 seconds. She also earned a bronze this month in Altenberg, Germany.
In addition, her remarkable run has been achieved with three different brakemen. Valois joined the sport just this fall.
"We learned last week that every hundredth-of-a-second matters so we just wanted to focus on pushing as hard as we could and not hold anything back," said Valois, a former track and field athlete at the University of Regina who impressed at recruitment camps this summer. "I’m overwhelmed. It is feels amazing and has been quite a year for sure."
The Canadian duo led by 0.12 after the first two runs on Friday and never looked back, laying down a new track record on their final run Saturday.
"Four consistently good runs are what won us gold," said Humphries, the favourite to repeat her Olympic victory next year.
"Now Sochi is my next goal."