"The governor of Carinthia and leader of the BZOe, Joerg Haider, died after a car accident early Saturday in Klagenfurt," Austria's APA news agency said.
"For us this is the end of the world," Stefan Petzner, the BZOe deputy leader, said.
Pronounced dead
Haider was taken to hospital but pronounced dead shortly after the accident.
He suffered serious injuries to his head and chest as his car flipped over several times.
Haider had been expected to attend a family celebration on Saturday, marking his mother's 90th birthday.
He headed the BZOe after turning the country's Freedom Party (FPOe) into a political force in the 1980s and 1990s and prompting EU sanctions against Austria in 2000.
Transformation
Haider changed from a young firebrand to an experienced politician in the past decade, helping the BZOe party, only founded in 2005, to its best result in general elections held last month.
Heinz Fischer, the Austrian president, described Haider's death as a "human tragedy".
Haider had led the right into a coalition government from 2000 to 2006.
His anti-foreigner comments and apparent endorsement of some Nazi policies had led to international condemnation.
In the 1990s, he reproached Austria's government by citing the "proper labour policies" of Adolf Hitler's Third Reich. On another occasion he referred to Nazi concentration camps in a parliamentary debate as "penal camps".
He once praised veterans of the murderous Waffen SS as "decent men of character".
But Haider denied Nazi tendencies.
'Outstanding talent'
Roland Adrowitzer, a correspondent with the Austrian broadcaster ORF, who knew Haider, told Al Jazeera that he was quite left leaning on social matters and regretted making any comments about Nazi policy years later.
"He was an outstanding political talent. You could like him or dislike him, but he never left anyone untouched," Adrowitzer said.
"He was very charismatic ... He presented himself in the [recent] election as a matured politician.
"He was one of the key players in Austrian politics."