Austrians are voting in a re-run of a presidential election which pits the leader of the far-right Freedom Party Norbert Hofer against former Green Party head Alexander Van der Bellen.
Martin Schulz, president of the European Parliament, on Sunday, congratulated Mr. Van der Bellen, saying, "His victory is a heavy defeat of nationalism and anti-European, backward-looking populism".
Eurosceptic populist parties in Germany, the Netherlands and France had voiced hopes that Hofer would win.
"I am infinitely sad that it didn't work out", Hofer said in a posting on his Facebook page less than an hour after polls closed. While the margin may change when final results are in, Austrian officials said the results gave Van der Bellen an unbeatable lead.
Austria was the first European Union nation to hold a presidential election since Trump's surprise victory last month in the U.S. In practice, Austrian heads of state have mostly asked the leader of the strongest party to form a cabinet.
The presidency is largely ceremonial but it would be another triumph for populist politics a month after Donald Trump's USA election victory and barely five months since the British chose to leave the European Union.
Much like the US President-elect Donald Trump, the former aeronautical engineer capitalized on fears surrounding Europe's worst refugee crisis since the second world war and immigration to boost his popularity.
Mr Van der Bellen will be the first ever Greens leader in Europe, and Austria's first to belong to neither main political party. They would see to it that Austria does not turn its back on Europe and would prevent any referendum on the euro - which would likely result in a clear vote for the euro anyway.
Strictly speaking, Austria's presidency is a ceremonial role, but Hofer has vowed that if he were to win, he would put his limited powers to full use, and to try and extend his control.
Van der Bellen said people should be guided by "reason not extremes" while Hofer urged voters to ensure a "safe Austria" for their "children and grandchildren".
A successful appeal by Hofer's euroskeptic and anti-immigration Freedom Party (FPÖ), however, meant that results were annulled.
"We all are Austria", he said in a television address.
Van der Bellen is running against right-wing populist Norbert Hofer.
His campaign message has varied from hard-line when talking to Freedom Party supporters to more moderate when trying to woo undecided voters disenchanted with the political establishment.
The election captured global attention, as a victory for Hofer in the wake of Britain's vote to leave the European Union could have boosted similar far-right eurosceptics across the bloc.