The 28-year-old student was the second athlete to start and she missed just one target on a glorious day of sunshine at Whistler Olympic Park before completing the course in 40 minutes 52.8 seconds.
Her nerve-racking wait then began as she was forced to watch the 85 skiers behind her make their way across the winding trails and through four rounds of shooting.
"I was really, really nervous because I had to wait until everyone had finished before I knew," Berger said after beating Kazakhstan's Elena Khrustaleva by 20.7 seconds.
Darya Domracheva of Belarus had to settle for the bronze.
"It was not a good time for me, but there were also many interviews that I had to do and I was being congratulated. When I understand I had won, it was such an amazing feeling."
Berger, who was flawless through the first three rounds of shooting, raised her right arm in celebration when she crossed the finish line before collapsing to the ground with fatigue.
"I was crying after the race but it was not bad tears but good tears," the Norwegian said, her eyes still reddened. "This is a dream I've had for so long."
Berger, whose best previous Olympic finish was fifth in the 4x6km relay at the 2006 Turin Games, took early control after shooting clean in the opening rounds of prone and standing.
Although she missed one target in the final round of standing shooting, she had built a big enough lead to seal the gold medal as Norwegian flags waved around the finish line and loud cheers rang out from her supporters.
"I thought I had lost a medal but then I was told that many of the others were missing shots too," Berger said of her missed target. "That made me work extra hard in the last leg."
When told she had earned her country its 100th Winter Olympics gold medal, she flashed a broad smile and said: "That is a very good feeling."
Khrustaleva was elated after clinching her first Olympic podium finish.
"This is the fruit of my labour, for all my hard work," the 29-year-old said. "I was shooting well and skiing well.
"The last lap was very hard. But I was patient and I did it. I just run, run and run."
Six-times world champion Magdalena Neuner of Germany, who won Tuesday's 10km pursuit and was bidding for her third medal of the Games, missed three targets on the way to 10th place.
Place of birth: Ringerike, Norway
Residence: Meraaker, Norway
Best previous Olympic result:
Fifth, 2006 Winter Olympics, 4x6km relay
Silver medallist, 2008 World Championships, 12.5km mass start
Silver medallist, 2006 World Championships, mixed 4x6km relay
Bronze medallist, 2009 World Championships, 15km individual
2x Bronze medallist, 2007 World Championships, mixed 2x6 + 2x7.5km relay, 4x6km relay
Third, 2008/09 World Cup, total
Background: She is also a student and is the sister of fellow international biathlete, Lars. Her hobbies include hunting, dogs and fishing.