Initial reports suggest he commited suicide.
Party colleague Janusz Maksymiuk told TVP television that he had met with Lepper yesterday but that there was "no sign that anything was wrong".
"Andrzej Lepper was a hard man. I can't imagine what would make him [commit suicide]," Maksymiuk added.
Chief of police spokesman Mariusz Sokolowski told the PAP news agency that all indications are that Lepper, 57 years old, hanged himself.
The once noisy, publicity-seeking rural trade unionist-turned politician became embroiled in corruption and sex scandals in his later years, which effectively ended his parliamentary career.
Lepper, born 13 June 1954, first made a name for himself as the leader of the Samoobrona (Self Defence) rural trade union, leading hunger strikes in the 1990s against farm repossessions and roadblocks for better deals for the farming community.
His maverick, populist style won him many supporters who felt excluded by the post-communist establishment and he eventually entered parliament as an MP under the Self Defence banner.
Lepper's political career reached a peak when his party entered into a coalition with Law and Justice after the 2005 general election. Still with his trademark perma-tan and quiff, he became agricultural minister and deputy prime minister.
His 'third way' politics - he argued Poland should form a new style of economy between capitalism and socialism - gained him some unusual friends, such as Belarus's authoritarian president Alexander Lukashenko and Venezuela's Hugo Chavez.
But trouble seemed to follow Lepper's career. He was accused of being involved in a land corruption scandal which eventually led to his dismissal as deputy prime minister and the downfall of the Law and Justice-led coalition.
He was also accused by a Self Defence party worker of asking her for sexual favours to advance up the party ladder.
In March this year a court in Lodz, central Poland, ordered that the sex case be re-tried on technicalities, although his party colleague, Stanislaw Lyzwinski received a prison sentence for rape, among other charges.
Lepper leaves behind a wife, Irena, and three children. (pg)