Mr Haider, 58, who earned worldwide notoriety for making statements sympathetic to Hitler's Nazi regime, suffered fatal head and chest injuries after the car he was driving plunged down an embankment near his home town of Klagenfurt.
Detectives are still investigating the cause of the crash, but said he was driving alone at the time in a government-owned vehicle.
The death of Mr Haider, who was governor of Carinthia province in southern Austria, comes less than a fortnight after a major resurgence in the far right's political support in the country, riding on a wave of anti-immigrant and anti-European Union sentiment.
At parliamentary elections last month, Mr Haider's Alliance for the Future of Austria polled 11 per cent of the vote, while the similarly-aligned Freedom Party, which Mr Haider founded but then split from, polled 18 per cent. The results meant nearly in three Austrians had voiced support for far-right movements, dismaying the country's liberal politicians.
Mr Haider's death may prompt concerns that political support will pass from him to the current Freedom Party leader, Heinz-Christian Strache, who is seen as a much more hardline figure. Mr Haider was originally Mr Strache's political mentor, but the two fell out as Mr Haider chose to pursue more moderate policies in recent years.
Mr Haider's spokesman, Stefan Petzner, said that he had been heading to a town near Klagenfurt for a gathering of his family to mark his mother's 90th birthday.
"This is for us like the end of the world," he added.
Born in Upper Austria, Mr Haider's father was a former member of Hitler's brown-shirted storm troopers, while his mother was a teacher who had been a Hitler Youth leader. Involved in politics since his teenage years, he caused an international outcry with a series of remarks where he appeared to imply an admiration for the Nazi era.
He once compared the employment policies of Austria's government with the "proper labour policies" of Adolf Hitler's Nazi Germany, and on another occasion he referred to Nazi concentration camps as "penal camps" rather than death camps.
Visits to see despots such as Saddam Hussein in Iraq and Colonel Gaddafi in Libya heightened his image as a pariah politician.
Such was the opprobrium he earned among fellow European statesmen that when the Freedom Party entered into a coalition government with the conservative People's Party in 2000, it triggered temporary European Union sanctions against Austria.
The coalition deal then fell apart, leading to an early election in 2002 in which the Freedom Party lost heavily, followed by a remake of the coalition.
Mr Haider then formed the breakaway Alliance for the Future of Austria in 2005, courting greater public acceptance by pursuing more moderate policies, but in a national election in 2006, the Alliance only just scraped past the 4 percent threshold to enter parliament.
Mr Haider is survived by his wife and two daughters.
DON'T MESS WITH THE NEW WORLD ORDER - DON'T EXPECT ANY POPULAR LEADER TO LIVE LONG
http://www.telegraph.co.uk/news/worldnews/europe/austria/3177339/Austrian-far-right-leader-Joerg-Haider-killed-in-car-crash.html
Haider had become more moderate. He started another party and split the so called Far Right vote which otherwise on pure arithmetic would be around 30 per cent. Would not be surprised if someone wanted him out of the way. He was driving alone, in good conditions, in a Mercedes, on a route he knew well, going to his mother's 90th birthday party (unlikely to have had anything to drink at all) and he goes over an embankment. Nor would I trust the police to come up with an impartial answer.