Bjoergen, the first Norwegian woman to win a 30km event at the Games, pulled ahead of Therese Johaug with a late burst of acceleration, while Kristin Stoermer Steira took the bronze.
After 10km, Johaug, Steira and Bjoergen split from the field and never looked back, with pre-race favourite Justyna Kowalczyk of Poland retiring midway through the race.
Bjoergen joins speed skater Lidia Skoblikova (former USSR) and cross-country skier Lyobov Yegorova (United Team and Russia) as the women with the most Winter Olympics gold medals.
It is the first clean sweep in Olympic cross-country skiing since Vegard Ulvang led Bjorn Daehlie and Terje Langli for a Norwegian sweep in the men's 30km classic in 1992.
(Reporting by Julien Pretot; Editing by Peter Rutherford)
