The ballots cast on Sunday were yet to be counted by Ukraine's Central Election Commission, but the exit polls coincided with the official results after the first round of elections which were held three weeks ago.
Shortly after the poll results were announced on Ukraine's state broadcaster Ukrinform, Poroshenko, conceding defeat at a press conference, said that he would help the new President prepare for the role between the official announcement of the election results and his inauguration.
"Next month, I will leave the office of the head of state. This is the decision of the majority of Ukrainian people. I accept this decision. I am leaving the office, but I want to highlight that I am not leaving politics. I will fight for Ukraine," Poroshenko was quoted as saying.
"My team and I are ready to support the president in everything that gets us close to the European Union and NATO. And between the official announcement of election results and his inauguration, I am ready to spend any length of time without any restrictions on helping the new president get up to speed," he added.
Meanwhile, Zelensky, on his part, pledged his supporters never to let them down.
"While I am not formally president yet, as a citizen of Ukraine I can tell all post-Soviet countries: Look at us! Everything is possible!" he noted.
The majority of the population holds Poroshenko responsible for the government's failure to tackle endemic corruption in the country.
Zelensky's electoral win shows the voters' deep-rooted disappointment in the Ukrainian government, rampant corruption, and a flagging economy. The support for Zelensky was largely seen as a protest vote against Poroshenko, who came to power in the aftermath of the 2013 pro-Western Maidan protests.
Prior to his bid for the presidency, Zelensky was best known for his role in the Ukrainian comedy series, "Servant of the People," where he played a schoolteacher who unexpectedly becomes the President of Ukraine after becoming famous for an anti-corruption rant that went viral on social media.
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