Comic Volodymyr Zelensky has won Ukraine's presidential runoff vote, defeating incumbent President Petro Poroshenko with more than 73 percent of the vote against about 25, according to official preliminary results.

Poroshenko conceded defeat on Sunday, April 21 at a press conference minutes after the exit polls were announced, saying 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," he said.

"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," said Poroshenko.

On his part, Zelensky pledged his supporters never to let them down.

He also said: "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!"

Zelensky, the star of the Servant of the People television sitcom, where he fights corruption as a teacher-turned-president, benefited from the Ukrainians' fatigue of mainstream politicians.

The majority of the population hold Poroshenko responsible for the government's failure to tackle endemic corruption in the country.