Bjoergen, a veteran sprinter, took the lead with about a third of the race left and crossed in three minutes 39.2 seconds, 1.1 seconds ahead of Poland's Justyna Kowalczyk.
Slovenia's Petra Majdic won bronze but deserved a special medal for extraordinary valour after conquering an excruciating injury over three races before painfully climbing to the podium.
"Today I won not only a bronze medal for myself, this is a gold with little diamonds on it," Majdic said. "I won a medal just getting to the start line."
The Slovenian, one of the pre-race favourites, plunged down a hill in practice but went on to struggle through two qualifying rounds and then finish third in the women's 1.4 km cross country sprint.
Majdic had hit a patch of ice on a corner and slid off the course during a warmup run earlier in the day.
"There was a big hole. I fell three metres. I fell on rocks. I broke one ski and both poles. I was screaming," she told a news conference, continuously wincing in pain.
"I was thinking, 'It's over,'" she said. "I thought it was over because I couldn't normally breathe or walk, or move."
The 30-year-old needed emergency medical attention for badly bruised back muscles and broken skin. Then she was told she should go to hospital.
"A part of me was screaming, 'I want to go to the start.' I didn't want to hear that I was finished," she said.
Majdic pushed herself through the pain barrier in the quarter-final and semi-final but ran out of stamina in the gold medal event, collapsing in a curled heap once she had captured Slovenia's first ever medal in cross-country.
The heroic achievement, and Majdic's clear state of agony afterward, overshadowed the gold medal-winning performance of Bjoergen.
Only after the final did Majdic agree to go to hospital, where an ultrasound exam revealed scrapes on her back, "a big punch on the muscles" but no broken bones.
Majdic, who walked gingerly into the post-race news conference with the help of an official, said it was unlikely she would race in Friday's 15km pursuit.
"I will try to focus myself for the 30km (on February 27). It's the only chance. All of the other races, no, they're gone because it's too painful," she said.
Bjoergen's gold was the first for Norway at the Vancouver Games and came as Norwegians were fretting about the lack of Olympic success.
Place of birth: Trondheim, Norway
Residence: Rognes, Norway
Previous major Olympic results:
Silver medallist, 2006 Winter Olympics, 10km
Silver medallist, 2002 Winter Olympics, 4x5km relay
3x gold medallist, 2005 World Championships, 30km mass start, 4x5km relay, team sprint
Gold medallist, 2003 World Championships, individual sprint
Silver medallist, 2005 World Championships, 15km pursuit
Silver medallist, 2003 World Championships, 4x5km relay
2x bronze medallist, 2007 World Championships, 4x5km relay, team sprint
Bronze medallist, 2005 World Championships, 10km
2x Champion, 2004/05, 2005/06 World Cup, overall
2x runner-up, 2003/04, 2006/07 World Cup, overall
Bjoergen started competing at the age of seven. Her partner Fred Borre Lundberg is an Olympic gold medallist in nordic combined.
The Norwegian has her own public relations specialist to deal with media pressures and allow her to train uninterrupted.