It was the sixth Olympic gold and 10th medal overall for the 33-year-old.
She finished in one hour 11 minutes and 5.2 seconds to lead home a Norwegian clean sweep with Therese Johaug in silver, 2.6 seconds back and Kristin Stoermer Steira winning bronze.
"It's incredible. I thought it would be hard but I've felt good," she said.
"I knew that I am stronger in the sprints, so I was waiting for them to attack on the last climb.
Bjoergen's gold saw her match the six golds won by Russian cross-country skier Lyubov Egorova, who also won three silvers over her career, and former Soviet speed skater Lidia Skoblikova.
She also matches the 10 medals won by fellow cross-country skiers Stefania Belmondo of Italy and Raisa Smetanina of the Soviet Uniion and the United team, but they have won fewer golds.
Bjoergen, who won three golds in Vancouver, pulled away from Johaug heading into the stadium and sprinted clear to follow up on her wins in the 15km skiathlon and the team sprint classic earlier in the programme.
It was 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.

The New Wales Link Path spans an extra 18 miles (29km), joining the route near the Cheshire border at Saltney Ferry.
It takes in four counties in all, stretching into Wrexham at Caergwrle and meeting the Offa's Dyke trail at Llandegla Forest in Denbighshire.
Flintshire council secured Â£30,000 in funding to pay for route-markers.
"If you are looking for a bit more of a challenge to walk around Wales, this route is for you," said councillor Bernie Attridge, cabinet member for the environment.
Work on Wales Coast Path, the world's first round an entire country, began in 2007 with the formal opening in May 2012.

Fed up with the way British Airways was handling the issue of his father's lost luggage, businessman Hasan Syed decided to complain about it.
But rather than just put out a normal tweet, he paid to have one promoted.
Using promoted tweets in this way could represent a new trend, experts believe.
The promoted tweet bought by Mr Syed reads: "Don't fly @BritishAirways. Their customer service is horrendous."
Promoted tweets are generally bought by advertisers who want to reach a wider audience. The paid-for tweet is given high prominence in the Twitter feed of the relevant company but otherwise acts as a normal message and can be retweeted by others.
Mr Syed purchased his paid-for tweet via Twitter's self-service ad platform for an undisclosed sum. He targeted New York and UK markets with the tweet.
The decision to highlight BA's customer service came following a trip his parents made from Chicago to Paris at the weekend, during which his father lost his luggage.
Six hours after the tweet went live, and was picked up by news website Mashable, it had been read by thousands of Twitter users, retweeted and commented on.
But it took another four hours for British Airways to pick up on it: "Sorry for the delay in responding, our twitter feed is open 09:00-17:00 GMT. Please DM [direct message] your baggage ref and we'll look into this."
The idea that the ad platform of large corporations can be hijacked by members of the public is an interesting trend, thinks Shashank Nigam, chief executive of aviation consultancy SimpliFlying.
"The implications are tremendous for the future of airline customer service, especially on social media," he said in his blog.
"These tools are easy to use and brand detractors have the same access to them as corporations. I'd guess that this cost less than a thousand dollars to buy and Mr Syed targeted it smartly," Mr Nigam told the BBC.
"Airlines are going to have to start having 24/7 customer services and maybe they need to train up call centre reps to respond to messages on Facebook and Twitter."
In this particular case, the tweet appears to have been successful.
"We would like to apologise to the customer for the inconvenience caused. We have been in contact with the customer and the bag is due to be delivered today," British Airways told the BBC.
Norwegian cross-country skier Marit Bjoergen won the women's 30km mass start to become the most decorated female Winter Olympian.
[NEXT_CONCEPT]
A new link has been added to the 870-mile Wales Coast Path at Flintshire for walkers seeking a "bit more of a challenge".
[NEXT_CONCEPT]
In a modern spin on the tale of David and Goliath, a disgruntled customer has found a new way to use social media to take on a big corporation.