Volodymyr Zelenskiy, an actor and comedian with no political experience other than playing the role of president in a TV series, has won a landslide victory in Ukraine’s presidential election, with near-complete counting showing he has won over 70% of the vote.

The incumbent, Petro Poroshenko conceded defeat on Sunday evening before results started coming in.

According to official results released on Monday morning, with 85% of the vote counted, 41-year-old Zelenskiy had won 73.4% of the vote, compared to Poroshenko’s 24.4%.

“I’m leaving office, but I want to make it clear that I’m not leaving politics,” said Poroshenko, acknowledging his failure to win a second term. “I will accept the will of the Ukrainian people,” he wrote on Twitter.

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Zelenskiy appeared in front of a crowd of journalists at his campaign headquarters as the polls closed and flashed an impish grin as he pushed his way on to the stage, accompanied by the theme tune to his television show.

“We did it together,” he said, thanking his wife, parents and campaign team. “Thanks to all the Ukrainian citizens who voted for me, and to all who didn’t. I promise I won’t mess up.”

The humiliating scale of the defeat for Poroshenko matched a series of polls over past weeks that have suggested Zelenskiy would win the runoff with ease.

The Zelenskiy camp said he had taken phone calls of congratulation from US president Donald Trump and French president Emmanuel Macron, among others.

Zelenskiy will take charge of a country facing numerous challenges, including a struggling economy and an ongoing war against Russia-backed separatist forces in the east that has claimed more than 13,000 lives.

He is best known for his role in the long-running Ukrainian television series Servant of the People, where he played a teacher unexpectedly elected to the presidency after an angry rant about corruption is posted online by his students.

During the campaign, he offered little information about his policies or plans for the presidency, relying on viral videos, standup comedy gigs and jokes in place of traditional campaigning.

Facebook Twitter Pinterest Petro Poroshenko concedes defeat in Ukraine’s presidential election as his wife, Maryna, looks on. Photograph: Efrem Lukatsky/AP

His campaign blurred the lines between the real-life Zelenskiy and his on-screen persona. Like the fictional president of his television series, Zelenskiy has promised to clean up politics and end the stranglehold of the oligarchy over Ukraine, but he has offered little by way of specifics.

Concerns have been raised about his close links to the controversial oligarch Ihor Kolomoyskyi. He issued a denial after Poroshenko dubbed him a “Kolomoyskyi puppet” – although many members of Zelenskiy’s campaign team also have links to the oligarch.

Journalists were offered free-flowing wine, a table tennis tournament and pumping music on Sunday evening at Zelenskiy’s campaign headquarters at a nightclub in an upmarket Kyiv business centre. However, there were no further details about his policies in his brief victory speech.

Zelenskiy has benefitted from voter dissatisfaction with Poroshenko, who came to office five years ago after the Maidan revolution. The billionaire confectionary magnate promised Ukrainians they would “live in a new way”, but the pace of change has been too slow for many.

The two candidates faced off in a chaotic televised debate at Kyiv’s Olympic Stadium on Friday evening, but the spectacle did not appear to change many minds. Poroshenko’s supporters tended to be worried about Zelenskiy’s lack of experience and potentially more amenable attitude towards Russia, while backers of Zelenskiy insisted that Poroshenko’s first term had been a failure and that he did not deserve another chance.

Voting on Sunday took place across the country, from the Carpathian mountains in the west to the war-torn Donbass region in the east, where soldiers on the frontline had an opportunity to cast their ballots.

“My nephew has been on the frontline in Donbass; what kind of country would put a clown in charge of its armed forces during a war?” asked Tetiana Hrytsenko, 61, who cast her ballot for Poroshenko on Sunday morning in Kyiv. A group of young people emerging from the same polling station said they had all voted for Zelenskiy.

There was little enthusiasm on display for either candidate, with most voters opting for the candidate they considered the least-worst option.

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“It’s like when you go to a cheap supermarket and all of the fruit is rotten, and you rummage around to find the least rotten piece,” said Anna, 32, an office manager who said she had waited hours in line to register for voting papers. On Sunday morning, she had still not decided which candidate she would vote for.

After voting in Kyiv, Zelenskiy was admonished by police for showing his ballot paper to the cameras. Displaying the ballot is illegal under Ukrainian law, and he now faces a fine of up to £24.

The chaotic but lively campaign in Ukraine has been watched closely in neighbouring Russia. While Russian state television has mocked the circus-like aspect of the vote, many have also looked on enviously at the lively debate and competitive atmosphere. On Sunday evening, Zelenskiy’s declaration of victory carried a message that could reverberate in the Kremlin.

“As a citizen of Ukraine I can say to all post-Soviet countries: ‘Look at us. Everything is possible’,” he said.