The vote pits centrist Warsaw Mayor Rafał Trzaskowski against Eurosceptic conservative contender Karol Nawrocki, who draws inspiration from US President Donald Trump.
Trzaskowski represents the ruling Civic Coalition (KO), while Nawrocki is backed by the opposition Law and Justice (PiS) party.
The outcome is seen as pivotal for Poland’s pro-European trajectory and its relations with neighbouring Ukraine.
Recent polls show the two candidates running neck and neck.
The race underscores the enduring divide between centrists and conservatives that has shaped Polish politics for more than two decades.
The vote also comes amid growing anti-establishment sentiment, with the far right making its strongest electoral gains to date.
The winner will serve a five-year term as head of state, overseeing defence and foreign policy and holding veto power over legislation.
A Trzaskowski victory would give a major boost to the government of Donald Tusk, a former top EU official, while a Nawrocki win would reinforce its uneasy cohabitation with the presidential palace.
Trzaskowski narrowly beat Nawrocki in the first round of voting on May 18.
Incumbent President Andrzej Duda, who has held office since 2015, is barred by the constitution from seeking a third term. His second term ends on August 6.
Polling stations will be open from 7 a.m. to 9 p.m. local time on Sunday.
A pre-election media blackout will begin at midnight on Friday, during which news outlets are prohibited from publishing opinion polls. Political campaigning is also banned until voting ends.
Nearly 700,000 Poles living abroad have registered to vote by absentee ballot, according to officials.
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Source: IAR, PAP