Casting her vote shortly after polling stations opened at 9:00 am (0600 GMT), a Helsinki resident who gave her name as Jenny said that she had only settled on who to vote for at the last minute.
With 100 percent of ballots counted, the Social Democrats, led by 56-year-old former trade union boss Antti Rinne, picked up 40 seats in parliament, after campaigning on a ticket of fierce opposition to the austerity imposed by the previous center-right government of Prime Minister Juha Sipila. Much of the debate in the run-up to the election has been about whether the next government should continue the current administration's public spending cuts.
And the nationalist True Finns party came in fourth, with 15.1 percent of the vote.
"For the first time since 1999 we are the largest party in Finland. Of course, the parties from the last government are going to suffer because of that now", she told AFP. "The Social Democratic Party's values are very important, it's the glue that will hold the government together".
However, in a tacit acknowledgement that the public mood has turned against further belt-tightening, Orpo has insisted the economy is now strong enough to allow for some more generous public spending. A record 1.5 million Finns - over a third of the electorate - had already cast their vote in advance of polling day.
In recent months, Finland's far-right Finns Party - previously languishing in fifth place in opinion polls - has surged in popularity to become the second- or third-biggest party, according to recent forecasts.
During the campaign, most parties expressed strong reservations about sharing a government platform with the Finns Party, which has called for the Nordic country to reduce its intake of refugees to "almost zero" and decries efforts to fight climate change as "hysteria".
However, Rinne said he "has questions" for the Finns Party and did not rule out cooperating with them to form a majority.
At a Finns Party rally on the eve of the vote in Myyrmaki, a disadvantaged suburb of the capital, a crowd of people, young and old, clamoured around party leader Jussi Halla-aho, asking for autographs and congratulating him on the campaign.
This could make the negotiations to build a government coalition particularly tricky. The Finns also want a revamp of its immigration policies.
Finland has a rapidly ageing population and declining birth rate, and the question of how to keep funding the country´s generous welfare state has been a key election battleground.
Yet the Social Democratic Party may face tough economic conditions in which to implement its anti-austerity promises: many economic forecasts suggest Finland´s GDP growth will slow in the coming years.
Meanwhile the Finns Party, which won 39 seats, had focused nearly entirely on an anti-immigration agenda under the leadership of hardline MEP Jussi Halla-aho, who also decried the "climate hysteria" of the other parties.
Immigration became a hot election topic following outrage in January over highly publicised reports of an alleged string of sexual assaults by immigrant men.