Prime minister Erna Solberg hosted a 60th birthday celebration attended by 13 people in late February, breaking her own government’s ban on gatherings of more than 10.
She has since apologised for her actions, stating that she was “very sad about what has happened”.
She has been fined 20,000 Norwegian crowns (£1,715) for the breach, police chief Ole Saeverud told a news conference on Friday.
Police suggested that the rules are being enforced particularly strictly in this case “in order to uphold the public’s trust” in the measures.
They said that they would not have issued a fine in most similar cases, but did so because Ms Solberg has led the government’s imposition of restrictions.
Emphasising the prime minister’s position of responsibility, the police chief said that “all are not equal in front of the law” despite the law being “the same for all”.
He explained: “It is therefore correct to issue a fine in order to uphold the general public’s trust in the rules on social restrictions.”
Her husband, Sindre Finnes, who police said helped plan the event and also broke the rules, was not fined alongside Ms Solberg.
The restaurant at a mountain resort where the celebration took place was not fined either, underlining the police’s desire to use the prime minister’s case to set an example.
“Solberg is the country’s leader and she has been at the forefront of the restrictions imposed to limit the spread of the virus,” said Mr Saeverud.
Norway, which has recorded some of Europe’s lowest rates of infection and deaths over the course of the pandemic, has suffered a surge in cases since the beginning of 2021.
The jump in infection numbers, caused by more transmissible virus variants, is part of a third wave sweeping Europe.
The government tightened restrictions in response to rising infection levels in March, with health minister Bent Hoeie blaming the rise on the coronavirus variant first discovered in Britain.