Andrzej Lepper, a Polish former deputy prime minister, was found dead at his Warsaw office on Friday.
Police believe the 57-year-old committed suicide.
The tough-talking Lepper rose to prominence in the 1990s. His firebrand rhetoric led many to compare him to French nationalist politician Jean-Marie Le Pen.
He often attacked Poland’s leaders for joining the European Union and exposing Polish farmers to increased competition.
Lepper mixed left-wing populist economic policies with hardline social views.
The former boxer once advocated castrating paedophiles and said in 2006 that “it is impossible to rape a prostitute.”
A Warsaw court convicted Lepper of sexually harassing a female aide that same year.
But he was never jailed. The conviction was quashed earlier this year and a retrial was ordered.