Volodymyr Zelensky, who plays a fictional president in a popular TV show, secured 30.4 percent of the vote on Sunday, early results showed. Petro Poroshenko, a billionaire magnate and Ukraine's current leader, received 17.8 percent.
With no-one expected to secure a majority when the final results are confirmed later on Monday, the two largely pro-EU candidates are set to go head-to-head in a run-off vote on April 21.
"If I win, we will (have) a strong democratic Ukraine — without corruption," Zelensky told CNBC's Steve Sedgwick in Kiev on Sunday.
"This is the biggest problem," Zelensky said, when asked whether fighting corruption would be a priority under his leadership.
'We don't want war'
In a country on the frontline of the West's standoff with Russia, the electorate has rallied behind an anti-establishment figure promising to combat deep-seated corruption.
Zelensky must now convince voters he is fit to lead a country at war and at the center of the West's tussle with Moscow.