The 29-year-old Bjoergen dominated the freestyle portion of the race and broke away from the field at the 9km mark to secure her third medal of the Games.
"I didn't think the speed on the skating was so high so I thought the chance was there," Bjoergen said. "But you never know. When I saw the gap, I knew I had the gold.
Sweden's Anna Haag took silver, while Justyna Kowalczyk of Poland grabbed bronze by sliding her right ski over the line one-tenth of a second before Norway's Kristin Stoermer Steira.
But the story of the day belonged to Bjoergen, who became the second Norwegian woman to win at least two golds at the Winter Games. Sonje Henie won three figure skating golds for Norway between 1928-36.
"I trained a lot for this," said Bjoergen. "I wanted to be in very good shape here. I thought this might be my last chance in the Olympics so I wanted to do everything right."
When Bjoergen crossed the finish line she screamed and pumped her fists in the air. She embraced Haag while Norwegian fans in the packed stadium howled for their hero.
"I don't think anyone could beat Marit today because she was really strong and really wanted a gold medal," said Haag, who finished nearly nine seconds back of Bjoergen. "Marit has fought for the podiums in almost every competition this year."
Bjoergen completed the course in 39 minutes 58.1 seconds on a sun-drenched day amid unseasonably warm temperatures at Whistler Olympic Park, about two hours from Vancouver.
She was in second place at the halfway mark when the race changed from the classic technique to freestyle, preferring to stalk the leaders rather than push to the front.
By the time the skiers entered the stadium for the final stretch there was no doubt Bjoergen was going to win her second gold. She had already won the individual sprint classic and placed third in the 10km free.
Haag said she could not find words to describe her feelings about winning the silver.
"I am so happy," she said. "The last hill I didn't think I could make it. I don't know where the strength came from."
The scoreboard said Steira had taken third place but this turned out to be a glitch and officials then announced the two women had tied in a photo finish.
"I was sitting in the snow. I was waiting. I was really tired because this last lap today was really, really tough. I was not thinking," said Kowalczyk, who captured a silver medal in the sprint classic.
Finally, around five minutes later, the 27-year-old student learned she had won the bronze.
"It was a very big emotion. Normally I am very bad at the finishing line and today was also not so good but I have long legs, I think two cm longer than Kristin's," she said.
"I felt sorry for Kristin. I think this was the fifth time she had a fourth place in the Olympics and that is not so nice," said Kowalczyk, the current World Cup leader.
Steira notched up three fourth places and a fifth in the 2006 Games.
"I was just fighting with all I had. Today it wasn't enough," the Norwegian said.
One of the race favourites, 10km free gold medal winner Charlotte Kalla, finished eighth but was never in contention after stumbling early in the race.
"I fell but I don't think that was the problem because I got too tired on the classic part so I had to let them go in front of me," said the Swede.
Place of birth: Trondheim, Norway
Residence: Rognes, Norway
Previous major Olympic results:
Gold medallist, 2010 Winter Olympics, individual sprint classic
Bronze medallist, 2010 Winter Olympics, 10km freestyle
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's gold in the 15km pursuit was her third medal of the Olympic Games in Vancouver.
She 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.