A crisis-packed year, fuelled by the refugee crisis and rising unemployment, has left the nation deeply polarised and pushed disgruntled voters away from traditional parties toward fringe groups.
The rift has found expression in Sunday's tense runoff, which sees 45-year-old Norbert Hofer of the anti-immigration Freedom Party (FPOe) running against the Green-backed economics professor Alexander van der Bellen, 72.
In last month's first round, Hofer -- a partially-paralysed gun enthusiast who is described as the FPOe's "friendly face" -- comfortably beat his rival by 35 percent to 21 percent.
But the candidates fielded by the Social Democrats (SPOe) and the centre-right People's Party (OeVP), which form Austria's ruling coalition, were knocked out of the race with just 11 percent.
Their dismal performance means that, for the first time since 1945, the president will not come from one of the two main camps.
And it raises a new risk of the winning candidate taking advantage of some of the role's never-before-used powers, like firing the government -- something Hofer has already threatened to do if the coalition fails to take a tougher line on migrants or boost the faltering economy.
"The real danger is an FPOe president who dismisses the government to clear the way for a blue republic," van der Bellen warned recently, referring to the party colour.
He also accused his opponent of being little more than a "henchman" for FPOe leader Heinz-Christian Strache.
But Hofer dismissed his remarks as "fear-mongering".
Photo: Hofer's web site
"I've always said the government's dismissal would only be a last resort," he said.
Nevertheless, the far-right contender also let slip a warning at a recent debate, declaring: "You'll see what's possible as a head of state."
But for political expert Peter Hajek, such powers mean little without public support.
"If the actions don't reflect public will, they are not a realistic political move," he told AFP.
Far-right joins forces
Exceptionally, no polls will be released ahead of the runoff after the first-round estimates proved disastrously wrong -- predicting that van der Bellen would defeat Hofer.
One thing is sure: the vote will be closely watched by the FPOe's European allies, including France's National Front (FN) whose leader Marine Le Pen has her sights firmly set on winning next year's presidential election.
"Magnificent result. Bravo to the Austrian people," she wrote on Twitter after Hofer's surprising victory.
Last summer, the FN and FPOe formed a bloc with other far-right EU parties to fight what they called the "Islamisation" of Europe.
More than a million people fleeing war and poverty in the Middle East and elsewhere arrived in 2015, triggering the continent's worst migration crisis since the end of World War II.
The influx, along with growing inequality, has proved a lethal mix for centrist governments across Europe as they struggle to keep voters from jumping on the populist bandwagon.
Game not over yet
In Austria -- which received some 90,000 asylum requests last year -- the main parties have been hemorrhaging support to the FPOe, which consistently scores more than 30 percent in opinion polls.
The demise means the SPOe and OeVP could fall short of being able to re-form their "grand coalition" at the next scheduled election in 2018. In the last vote three years ago, they only just managed to secure a majority.
The FPOe has repeatedly called for snap elections, in the hope it can join the government as it did back in 1999 under Strache's predecessor, the late, SS-admiring Joerg Haider.
However, while the reins of power may seem tantalisingly close to Hofer, a win is not yet guaranteed.
One twist was the unexpected resignation of Chancellor Werner Faymann of the SPOe on May 9. His successor, popular ex-railway boss Christian Kern, has backed van der Bellen and made clear he would not accept the FPOe as coalition partner.
"After the first round, Hofer was the clear favourite but now there's been a change in government, which has to be considered," political analyst Hubert Sickinger told AFP.
"We have to see if there will be a 'Kern effect' on voters."