It's the country's longest-ever presidential campaign and the most turbulent in its post-war history.
First there were six
The first round started with six candidates on April 22. Since 1945 the presidency -- a largely ceremonial job -- had always gone to the ruling centrist camp, made up of the Social Democrats (SPÖ) and the conservative People's Party (ÖVP).
But this year, disgruntled voters kicked out the coalition's two candidates and flocked instead to Hofer of the anti-immigration Freedom Party (FPÖ), who won with 36 percent.
The only person blocking his path to becoming the EU's first far-right head of state was runner-up and ex-Green party chief Van der Bellen.
The SPÖ's catastrophic performance would cost the scalp of its chancellor, Werner Faymann, who quit in early May.
And the winner is...
On the evening of May 22, Hofer beamed into TV cameras: the 45-year-old had
just won the tense run-off, projections showed.
But over the next 24 hours, his hopes were crushed. The postal votes, which are traditionally tallied the day after the polling station count, gradually swung the outcome in Van der Bellen's favour.
In the end, the 72-year-old economics professor beat his rival by just over 31,000 votes.
Van der Bellen -- as well as many European leaders -- breathed an audible sigh of relief
"I want to be a nonpartisan president for all the people in Austria," the new president-elect solemnly vowed in his first speech.
But his ambition to heal "national rifts" would be put on hold. The FPÖ filed a legal challenge in June against the result over alleged procedural problems discovered in numerous constituencies.
Reported breaches included postal votes being opened too early, as well as "non-Austrians" or under-16s casting ballots.
Siding with the FPÖ, the Constitutional Court annulled the May result in July, and ordered a re-run for early October.
The verdict was a big blow to the government, prompting Austria's interior minister to say he was "ashamed... of this sloppiness".
Newspapers were also outraged, with one tabloid calling Austria a "banana republic -- probably the only country outside Africa and Kazakhstan that is unable to count votes properly".
A school book publisher was forced to pull 2,500 freshly printed history tomes naming Van der Bellen as Austrian president.
The ruling meant the two candidates had to reach deeper into their pockets, print new election posters, hop back on the tour bus, and shake more hands. Then the election came unstuck again in September.
Barely back from its summer recess, the government announced that the October 2 re-run would be postponed to December because of faulty glue on postal vote envelopes.
To be on the safe side, parliament decided the winner would only be sworn in in late January to give authorities sufficient time to investigate any potential new issues.
A police probe later revealed the faulty glue came from neighbouring Germany.
Creation of a new German word
Van der Bellen took the re-run news in his stride, marching through crowds of supporters to Daft Punk's tune "One more time".
Hofer meanwhile turned to religion and plastered the slogan "So help me, God" across his posters.
The longer the contest lasted, the more surreal it became. At one point, Van der Bellen, a heavy smoker, was forced to dispel cancer rumours by releasing his medical records proving he had "wonderful lungs".
During Thursday's final TV duel, Hofer accused his rival -- who has Russian roots -- of having been a Cold War spy for the Soviet Union -- claims Van der Bellen dismissed as "ridiculous".
By the time Sunday's vote gets under way, the election will have cost an estimated €15 million.
Since April's first round, 45,000 voters have died while another 45,600 have turned 16 and are now eligible to cast their ballot.
The race has also led to creation of a new German term: Bundespräsidentenstichwahlwiederholungsverschiebung, which translates as "the delay in the repetition of the presidential re-run."