The 25-year-old from St-Ferreol-les-Neiges, Que., narrowly held off Norway's Martin Johnsrud Sundby to win the men's 30-kilometre race.
"This has been the best season of my life," Harvey said. "Obviously we didn't have that magic we needed at the Olympics which was the goal, but I have five podiums this year, three victories, and this just reconfirms all of the work we did in the summer."
Therese Johaug took a big step toward securing the overall cross-country World Cup title by beating Norwegian teammate Marit Bjoergen in the women's 15-kilometre skiathlon race.
Harvey, whose best finish last month in Sochi was 18th, powered his way up the hills on the 2015 world championship course Saturday and took advantage of the fast glide on his skis in the downhill. He carried the pace until one kilometre to go when he shuffled to the side and moved into the back to draft on the final downhill and slingshot to gold.
He beat Sundby in a sprint to the finish, crossing in one hour 18 minutes 7.6 seconds. The Norwegian finished just 0.12 seconds behind. Alexander Legkov of Russia was third, 1.76 seconds behind.
Harvey has found success before in Falun, capturing his first World Cup title there in 2012. It's the same venue where his father Pierre won his first of three World Cup medals in 1987.
"I just love racing and Falun is always at the end of the season," Harvey said. "I think some guys when they feel tired at the end of the year they shut down in the head a bit, but I just love to race. When there may be tired bodies at the end of the season, I like to keep going.
"The course is so hard and it requires sustained work, and I just enjoy racing here."
Harvey is fourth in the overall World Cup standings with the final 15-kilometre skate-ski pursuit race scheduled for Sunday.
Devon Kershaw of Sudbury was 12th Saturday, while Ivan Babikov of Canmore, Alta., was 23rd.
Johaug, meanwhile, won the women's race in 41:08.9 to beat Bjoergen by 33.6 seconds, with Finland's Kerttu Niskanen finishing third. Andrea Dupont of Timmins, Ont., was 45th.