Kotleba has a range of controversial views: he considers NATO a terrorist organisation; he has been arrested for hate speech against the country's large and impoverished Roma minority; and he has in the past denied the Holocaust.
He is also a trenchant Eurosceptic, believing that Slovakia should dump the euro currency.
The 36-year-old has also spoken warmly about former President Jozef Tiso, who agreed to send tens of thousands of Jews to Nazi death camps during World War II. He recently traded in his Nazi-style uniform for a suit and used the fallout from the economic slowdown to lash out at the Roma community.
Kotleba won in the election for governor of the Banská Bystrica region in a run-off, beating the ruling party centre-left Smer party's candidate, incumbent Vladimír Maňka, leaving most of the country frozen in disbelief, according to the Slovak Spectator.
Maňka was also backed by the Greens, the Movement for Democracy (HZD), the Movement for a Democratic Slovakia (HZDS), the Party of Modern Slovakia (SMS), the Christian Democratic Movement (KDH) and the Party of Hungarian Communities (SMK), and Most-Híd.
The Slovak Democratic and Christian Union's (SDKÚ) regional leaders, namely its regional head Ľudovít Kaník, who came third in the first round of the governor election and thus did not move on to the run-off, did not recommend that the public vote for Maňka.
Prime Minister Robert Fico, the leader of Smer, was quick to blame the SDKÚ and another rightist party, Freedom and Solidarity (SaS) for not supporting the Smer candidate against Kotleba. Smer is affiliated with the centre-left Party of European Socialists (PES), while the SDKÚ is affiliated with the centre-right European Peoples’ Party (EPP).
“Voters of the right surely voted for Kotleba in order to see Smer lose,” Fico said as quoted by the Sme daily, adding that for the right even “Antichrist, Satan, Hitler, Mussolini” would be better than Maňka.
Observers smashed the reaction of the prime minister as demagogic, saying that all politicians carried their part of responsibility for the development.
Slovak President Ivan Gašparovič said he was "surprised by the result" and called it "a warning for politicians not to be oblivious and indifferent to problems that people have been facing for a long time".
Human rights activists and Jewish groups sounded the alarm over Kotleba’s election. The Paris-based European Jewish Congress urged EU leaders on Monday to "reverse the momentum achieved by neo-Nazi political parties in Europe ... before it's too late."
"The neo-Nazis are gaining many political victories and are using the democratic system against democrats. Democracy has to fight back," EJC President Moshe Kantor declared.