Whether Hofer can beat independent ecologist Alexander Van der Bellen in September remains to be seen, particularly if after Britain's Brexit vote Hofer takes the gamble of making a possible Austrian EU exit a big issue, experts said.
The new vote follows a ruling by Austria's highest court on Friday in which Van der Bellen's narrow May 22 victory was declared null and void.
Van der Bellen scraped home in the ballot with just 30,863 votes over Hofer of the anti-immigration Freedom Party (FPÖ) for the largely ceremonial but coveted presidency.
Early results for Hofer, seen as a moderate face of the FPÖ, had put him slightly ahead, but after postal votes were counted Van der Bellen was declared the winner, sparking relief among centrist parties in Austria and across Europe.
The FPOe, which is topping opinion polls ahead of the next scheduled general election in 2018 on the back of concerns about immigration, launched a legal challenge on June 8 claiming "terrifying" irregularities.
After dozens of witnesses detailed what Interior Minister Wolfgang Sobotka called widespread "sloppiness", the court found that postal votes in 14 areas were opened too early or by unauthorised persons, and so could potentially have been doctored.
Austria's interior minister said Saturday he was "ashamed" after the country's highest court declared the result of May's presidential election null and void because of widespread procedural
Friday's ruling by the Constitutional Court invalidating the outcome of the May 22 election means that Norbert Hofer of the Freedom Party (FPÖ) will have another shot at becoming the EU's first far-right president.
I am "disappointed, ashamed... The fact that this sloppiness and breaking of the law took place has shaken me massively," Wolfgang Sobotka told Ö1 public radio, saying he was "embarrassed".
The court's ruling, triggered by an FPÖ legal challenge, found that postal votes in 14 areas -- or 78,000 votes -- were opened too early or by unauthorised persons, and so could in theory have been tampered with.
Since this represented more than double the independent ecologist Alexander Van der Bellen's winning margin of just 31,000 votes, the court said that the election must be held again. No date has been set, but it is expected to be in September.
National newspapers on Saturday were outraged. The Oesterreich tabloid said that the ruling showed that Austria is a "banana republic -- probably the only country outside Africa and Kazakhstan that is unable to count votes properly."
For the re-run, Sobotka said that media outlets and research institutes will not be provided with partial results before voting officially ends -- unlike during the first take of the election on May 22.
The government would also consider changes to Austria's electoral law, the minister said.
"At the next election, there will no results before all votes, including postal votes, have been counted," he said.
Possible other changes could include allowing postal votes to be counted on the day of the election, and not the next day like now.
The Kurier daily reported that Sobotka wants to have election observers from the Organization for Security and Co-operation in Europe (OSCE) present.
The body decided after reviewing preparations not to send observers on May 22, the paper said.
Voter turnout key
The annulment ruling means that Van der Bellen's planned inauguration set for July 8 has been scrapped, and sets in motion what is likely to be a hard-fought summer election battle of high drama.
Van der Bellen voter Hermann, 36, waiting for a bus in central Vienna, said he thought Van der Bellen would clinch victory again -- but only just.
"I don't think people will vote differently. The two camps are so far apart that we will get a similar result," he told AFP. "I don't think the result will be any different," agreed hairdresser Daniel Huber, 26.
But experts said that voter turnout will be key, as well as which side has more money to invest in its campaign after the high costs of the May election depleted their coffers.
"It will depend which side is the more successful at mobilising its voters," David Pfarrhofer from the Market polling institute told AFP. His "gut feeling" is that some typical Van der Bellen voters -- younger, more educated, urban -- might not vote.
Veteran expert Anton Pelinka said that Van der Bellen has a bigger task on his hands getting supporters out to vote than his gun enthusiast challenger, who walks with a cane since a 2003 paraglider accident.
"Support for Van der Bellen was much more heterogenous than for Hofer. Hofer can rely on voters from one party (the FPÖ) but Van der Bellen needs a complex alliance of the centre-right and the left," Pelinka told AFP.
In May, Hofer focused on issues like wanting more direct democracy rather than the record 90,000 asylum applications in Austria last year. But he still says Islam "has no place in Austria" and opposes gay marriage.
Observers say that beneath the smooth image lurks a far-right idealogue who has already threatened to seize upon never-before-used presidential powers to fire the government if it fails to get tougher on migrants or boost the faltering economy.
And this time, after British voters' shock decision on June 23 to leave the European Union, Hofer may decide to make a possible Austrian exit a vote-winner.
After the Brexit vote he came out in favour of a referendum if the EU fails to reform enough in the next year. Van der Bellen -- a wartime child refugee from the Soviet Union -- is staunchly in favour of Austria remaining in the bloc.
Political expert Hubert Sickinger said that if Hofer makes an EU exit a big issue, Van der Bellen would likely profit. "A solid majority in Austria is against leaving the EU," he told AFP.