Incumbent Andrzej Duda has won the Polish presidential election by a wafer-thin margin, with 99.7% of ballots counted.
He narrowly beat pro-European liberal Warsaw mayor Rafal Trzaskowski with 51.2% of the vote, the country's election commission said.
Turnout for the second round of the election was reportedly 68.2%, the highest of any presidential poll since the start of free elections in post-communist Poland in 1989.
Electoral commission chiefs said on Monday morning that they were unsure when complete results would be announced, with some polling stations yet to submit their counts, but with over 99% of the votes accounted for, the final result was not expected to change.
Duda is backed by the ruling right-wing Law and Justice party and pushed traditional values and social spending on the campaign trail in mostly-Catholic Poland.
Declaring victory overnight on Sunday he thanked "all my compatriots who voted in this election, those who made a lot of effort to be able to cast their ballots."
"I thank you all from the bottom of my heart because such a turnout is a beautiful reflection of our democracy," he added.
Addressing supporters in Warsaw's Old Town, Trzaskowski had sounded optimistic about his chances of securing the presidency on Sunday evening, telling the crowd, "We will wake up tomorrow in a completely new Poland."
He added: "All we need is to count the votes. The night will be tense but I am certain that when the votes are counted, we will win."
Over 180,000 Poles were registered to vote in the UK, with 48.4 per cent voting for Trzaskowski in the first round of the presidential election, compared to just 15.5 per cent for Duda.
The result of the vote is significant for the Eastern European country, which has become polarised under the current government led by Duda's allies, the Law and Justice (PiS) party.
The ruling party has been praised by Poles for their social policies which have lifted many out of poverty, particularly in rural communities. But critics have accused the government of exacerbating social rifts by targeting minorities, like Jews and the LGBT community, as well as eroding democratic norms since it took power in 2015.
The latter has brought Poland into conflict with the European Union, which raised concerns about the implementation of controversial judicial reforms. If elected, pro-EU Trzaskowski vowed to repair the strained relationship between Warsaw and Brussels.
Due to the pandemic, the election was held under tight security measures with voters required to use their own pens to cast their ballot, wear face masks and observe social distancing in polling stations.