The European Union-sceptic FPO held a slim lead in opinion polls for months over Chancellor Karl Nehammer's ruling conservative Austrian People's Party (OVP) in a campaign dominated by immigration and worries about the economy.
Led by Herbert Kickl, the FPO was projected to secure 29.1 per cent of the vote, ahead of the OVP on 26.2 per cent and the Social Democrats on 20.4 per cent, a projection by pollster Foresight for broadcaster ORF showed after polls closed.
A separate projection by pollster Arge Wahlen also had the FPO coming first, winning by about 4 percentage points, a bigger winning margin than final polling had indicated.
"What's at stake is whether the FPO will appoint the chancellor or not," Kathrin Stainer-Haemmerle, a political science professor at the Carinthia University of Applied Sciences, said.
"Should that happen, then I have to say the role of Austria in the European Union would be significantly different. Kickl has often said that (Hungarian Prime Minister) Viktor Orban is a role model for him and he will stand by him."
Chancellor Karl Nehammer has rejected a coalition with the FPO if Herbert Kickl remains its leader. (AP PHOTO)
The winner will not have an absolute majority but will claim the right to lead a coalition.
The projections were met with cheers at an FPO event in Vienna, with party staff and activists jubilant.
Kickl's victory may prove pyrrhic, as the 55-year-old is a polarising figure under whom other party leaders have refused to serve.
He has given no indication so far he could step aside to ensure his party leads the government.
An FPO victory would make Austria the latest EU country to register surging support for populist conservatives after gains in countries including the Netherlands, France and Germany.
The FPO, which is critical of Islam and pledges tougher rules on asylum seekers, won an Austria-wide vote for the first time in June when it beat the OVP in EU elections.
The party is a long-established political force but Sunday's projected result, if confirmed, would be its best yet in a parliamentary election - beating the 26.9 per cent it scored in 1999.
The OVP, which also backs tougher immigration rules and tax cuts, is the only party open to forming a coalition with the FPO.
However Nehammer says his party will not join a government with Kickl in it.
Sarah Wolf, a 22-year-old graphic designer and Austrian Communist Party supporter in Vienna, said ahead of the vote she was worried what an FPO victory would mean.
"What most scares me if the FPO really does get the most votes is we get something like Viktor Orban: a slow, gradual reduction in media diversity, democracy and understanding," she said.
"There are just so many really dangerous signs."
Viktor de Lijzer, a 17-year-old soldier who supports the FPO, said the party was best placed to fix what he saw as too much criminal violence spurred by immigration.
President Alexander Van der Bellen, who oversees the formation of governments, has voiced reservations about the FPO because of its criticism of the EU and its failure to condemn Russia's invasion of Ukraine.
The party opposes EU sanctions on Russia, citing Austria's neutrality.
He has hinted he might thwart Kickl, saying the constitution does not require him to ask the first-placed party to form a government even though that has long been the convention.
In its election program, titled "Fortress Austria," the Freedom Party calls for "remigration of uninvited foreigners" for achieving a more "homogeneous" country by tightly controlling borders and suspending the right to asylum via an "emergency law".
"The voter has spoken. Change is wanted in our country," FPO general secretary Michael Schnedlitz said although he acknowledged that "we don't have the final result yet".
with AP
7°C