The 36-year-old went out in Helsinki on Saturday (4 December) until the early hours after her foreign minister Pekka Haavisto tested positive, but she was initially told she didn't need to isolate because she was fully vaccinated.
The Social Democratic PM - who became the world's youngest prime minister when she elected to lead a centre-left coalition with four other parties in 2019 - said a subsequent text advising her to avoid social contact was sent to her work phone, which she hadn't taken out with her.
Evidently, Marin was keen to let her hair down, with eyewitnesses telling Seiska magazine that she was dancing at Butcher's club until 4am.
When she eventually saw the text she said she urgently got tested, and the result came back negative.
Initially, Marin defended her actions, arguing she had followed the guidance of her secretary of state, but in a Facebook post on Monday (6 December) she said she should have double-check the guidance and used better judgement.
"I'm really sorry that I didn't understand how to do this," she wrote.
Finland has recorded some of the lowest levels of Covid in Europe throughout the pandemic, recording about 196,000 cases and 1,384 deaths.
However, cases have climbed in recent weeks and infections are now at a record high, with 308 new cases per 100,000 people in the last fortnight.
The story in the UK is similar - in that the PM is under fire and Covid cases are rising sharply.
Boris Johnson has come under intense pressure over a Covid restriction-breaching Christmas party last year, which he has repeatedly denied took place, but which ever mounting evidence suggests did happen.
His former spokesperson Allegra Stratton tearfully resigned yesterday (Wednesday 8 December) following a leaked video showing her joking about the party and there are calls for Johnson to follow suit.
He seems intent on staying put for the time being though, and has announced that the country will be moving to its 'Plan B' amid rising Covid levels.
From Monday (13 December), people must return to working from home wherever possible, and vaccine passports will be needed to access nightclubs and large events, such as football matches and gigs.
And from tomorrow (Friday 10 December), face masks will become mandatory in most public indoor venues, including in theatres and live venues, although they will not be required when it is not practical - such as when eating, drinking, exercising or singing.Featured Image Credit: Alamy