Polish nationalist opposition candidate Karol Nawrocki won the second round of the country's presidential election with 50.89 per cent of the votes, the electoral commission said early on Monday on its website.
His rival, Rafal Trzaskowski, the liberal Warsaw mayor and an ally of the government led by Donald Tusk, got 49.11 per cent.
Nawrocki, 42, a eurosceptic historian and amateur boxer who ran a national remembrance institute, campaigned on a promise to ensure economic and social policies favour Poles over other nationalities, including refugees from neighbouring Ukraine.
While Poland's parliament holds most power, the president can veto legislation, and the vote was being watched closely in Ukraine as well as Russia, the United States and across the European Union.
On social media platform X, current President Andrzej Duda, also a conservative, thanked Poles for going to vote in large numbers. Turnout was 71.31 per cent, the electoral commission said, a record for the second round of a presidential election.
"Thank you! For participating in the presidential elections. For the turnout. For fulfilling your civic duty. For taking responsibility for Poland. Congratulations to the winner! Stay strong Poland!" Duda wrote.

Trump touts $5,000 payout if Republicans win as Vance waits in wings
Search expands after Philippine ferry fire kills five and leaves dozens missing
Trump says Iran war to end after US midterm elections
At least 20 killed in cargo vessel fire at China shipyard, state media reports
US military says it struck vessel in Caribbean, killing 3
At least 14 killed in explosion at weapons depot in Syria
US hits five Iranian oil tankers after attack on Navy ships
UK gives air traffic provider a week to probe outage that halted flights
