Polls show Volodymyr Zelensky, a 41-year-old standup comic and television star with no political experience, handily defeating President Petro Poroshenko in a second-round of voting on Sunday.
The actor’s bid started as a long shot but he leapfrogged establishment candidates amid public frustration over corruption, a stalling economy and a separatist conflict in the country’s east.
The debate, set to take place in Kiev’s 70,000-seater Olympic Stadium Friday evening, will be the first and only policy head-to-head of the campaign.
Poroshenko, 53, says he is the only candidate who can take on Russia’s President Vladimir Putin and is expected to strike out at the inexperience of the untested Zelensky.
He is also expected to slam his rival’s close ties to controversial oligarch Igor Kolomoysky.
Zelensky will likely attack what he says are his rival’s half-hearted attempts at rooting out corruption and cementing the rule of law five years after a popular uprising ousted a Kremlin-backed regime.
The debate will bring to a close a race that has seen the two main candidates exchange insults and undergo drug tests at the younger man’s insistence.
Zelensky, whose previous political experience has been limited to playing the president in a TV show, said he was ready to face the Ukrainian leader in the debate.
“I am not a coward,” he said in a rare television appearance late Thursday during which he also unveiled his team.
Poroshenko has previously called Zelensky a “cat in a bag”, or unknown entity.
But Zelensky said that “a cat in a bag is better than a wolf in sheep’s clothing,” noting Ukrainians were yearning for change.
A survey by the Rating pollster released Thursday showed Zelensky winning 73 percent of the vote against only 27 percent for Poroshenko.
The stakes are high for the country of 45 million people seen as a buffer between the European Union and Russia.
Ukraine is mired in a smouldering war with Moscow-backed separatists in the industrial east, a conflict that has claimed 13,000 lives.
A parliamentary election is also due to be held in October.
Kremlin spokesman Dmitry Peskov said he did not know whether President Vladimir Putin would tune in to watch the debate but added he himself might enjoy a “curious spectacle”.
In a dramatic video address, Poroshenko on Thursday begged for forgiveness and a second chance.
“What did not work out hurts the most,” he said.
He added that because of the conflict with Russia, it would be “very risky to experiment with the post of the president and commander-in-chief”.
Supporters credit Poroshenko — who took power after a popular uprising in 2014, with implementing economic reforms — rebuilding the army, securing an Orthodox Church independent of Russia and winning visa-free travel to Europe.
However, he won just over half of Zelensky’s vote share in the first round of the election last month.
The West is closely watching the race amid concern that a new government might undo years of reforms.
French President Emmanuel Macron hosted both candidates for separate talks last week.
The main risks associated with a Zelensky presidency are “policy incoherence stemming from inexperience” and “undue influence from oligarchs or Russians,” a former Western diplomat told AFP.
In a startling development on Thursday, a Kiev court ruled that the Poroshenko government’s 2016 decision to nationalise the country’s biggest lender as part of a reform drive was illegal.
The bank, PrivatBank, was owned at the time by Kolomoysky who owns the channel that broadcasts several of Zelensky’s shows.
Poroshenko warned that Ukraine risked defaulting on its debt if the bank were handed back to the tycoon after his government spent nearly $6 billion on recapitalising the lender.
The EU, Washington and the World Bank said in coordinated statements they were closely monitoring the situation.