Milei has railed against the "thieves" of the political elite, praised gangster Al Capone for his free market credentials and on live TV smashed a piñata of the central bank, which he blames for Argentina's triple-digit inflation and intends to shut.
The 53-year-old self-proclaimed anarcho-capitalist is now pollsters' narrow favorite to win a run-off election on Sunday against Peronist economy chief Sergio Massa, his combative stance a lightning rod for voter anger at the country's worst economic crisis in decades.
"We will put an end to the parasitic, stupid, useless political caste that is sinking this country," Milei said in a speech after finishing in first place in primary elections in August, a result that shook up a political landscape long dominated by two parties.
His aggressive and theatrical style has led some to compare him to Donald Trump in the United States or Jair Bolsonaro of Brazil.
But he is a unique product of Argentina, where an entire generation has grown up under an economy in a semi-permanent state of crisis. That has sharpened this year, with inflation heading towards 150%, a sliding currency and rising poverty.
Against that backdrop, Milei and his Liberty Advances coalition have seen a dramatic rise in support, especially among the young. His campaign on social media has been helped by his colorful antics and quotes.
"He is the change that Argentina needs," said 28-year-old Milei voter Ayrton Ortiz at a rally in Buenos Aires.