Comedian Volodymyr Zelenskiy will become Ukraine's next president after the current leader Petro Poroshenko conceded defeat.
Mr Poroshenko said he did not plan to quit politics altogether but will be leaving his position as president next month.
Results from the an poll, released Sunday after voting stations closed, showed Mr Zelenskiy receiving 73.2% of the nationwide vote.
Meanwhile, it said current president Mr Poroshenko received 25.3%.
The poll was based on more than 13,000 responses to face-to-face questions at 300 polling stations places as of 6 pm, two hours before the polls closed.
The victory of Mr Zelenskiy, 41, is a bitter blow for incumbent Mr Poroshenko.
He had tried to rally Ukrainians around the flag by casting himself as a bulwark against Russian aggression and a champion of Ukrainian identity.
If the poll is correct, Mr Zelenskiy, who plays a fictitious president in a popular TV series, will now take over the leadership of a country on the frontline of the West's standoff with Russia following Moscow's annexation of Crimea and support for a pro-Russian insurgency in eastern Ukraine.
He has also promised to end the war in the eastern Donbass region as well root out corruption amid widespread dismay over rising prices and falling living standards, though his tactics to achieve these aims are unclear.
