Slovakia is set to vote for a new president, with front runner, Zuzana Caputova facing European Union Commissioner Maros Sefcovic.
The two candidates got the most votes in the first round a fortnight ago, but failed to gain the 50% needed to win.
If elected, Ms Caputova, a lawyer and anti-corruption activist with almost no political experience, will be the first female Slovak president.
The election follows the murder of an investigative journalist last year.
Jan Kuciak was looking into links between politicians and organised crime when he was shot alongside his fiancée in February 2018.
The BBC’s Rob Cameron in Bratislava says that although the presidency is mainly a ceremonial role, Ms Caputova is framing the election as a struggle between good and evil.
She cites Mr Kuciak’s death as her motivation for getting into politics and has led a campaign focusing on anti-corruption.
Ms Caputova gained prominence as a lawyer, when she led a case against an illegal landfill lasting 14 years.
Aged 45, a divorcee and mother of two, she is a member of the liberal Progressive Slovakia party, which has no seats in parliament.
In a country where same-sex marriage and adoption is not yet legal, her liberal views promote LGBTQ+ rights.
Her lack of experience places her in stark contrast with her opponent, Mr Secovic, who is a diplomat and vice president of the European Commission.
He is a member of the ruling Smer-SD party, which is led by Robert Fico, who was forced to resign as prime minister following the Kuciak murder.
In the first voting round, Ms Caputova won 40% of the vote, with Mr Sefcovic gaining less than 19%.
She is leading by a wide margin in opinion polls.