The projections showed the 78-year-old incumbent swept 54.6 percent of the votes with six other candidates -- all men -- lagging far behind.
The final official result is not expected until Monday.
Campaigning on a slogan of "clarity", Van der Bellen had been widely tipped to clinch a second mandate, with his six challengers -- all men -- lagging far behind.
"It would be nice if we had clarity today -- nice for Austria, nice for us -- if we can then fully concentrate on the diverse tasks ahead, the multitude of crises... that we in Austria, in Europe, are facing," the 78-year-old economics professor said after casting his ballot earlier on Sunday in central Vienna.
Polls ahead of the election had suggested the pro-European liberal would secure more than 50 percent of the vote, thus avoiding a run-off.
READ ALSO: Van der Bellen could avoid run-off in presidential election as still strong favourite: poll
Some 6.4 million people were eligible to cast their ballots from the country's total population of nine million.
Polling stations in Vienna and much of the rest of the country opened at 7:00 am local time (0500 GMT) with a few opening as early as 6:00 am, and closed at 5:00 pm (1500 GMT).
The presidential post, which has a term of six years, is largely ceremonial.
'Consistency'
"I am in favour of consistency," 73-year-old retiree Monika Gregor told AFP outside a Vienna polling station earlier on Sunday, saying she had voted for Van der Bellen and thought he was "very clever".
Posters proclaim the former Greens leader to be "the safe choice in stormy times" as the ripple effects of Russia's invasion of Ukraine push up inflation throughout Europe.
Van der Bellen was running again as an independent but he has the explicit or implicit backing of Austria's major parties except the far-right Freedom Party (FPOe), which fielded its own candidate, Walter Rosenkranz, who, according to the projections, got 18.9 percent.
Also standing for the presidency was 35-year-old punk rocker Dominik Wlazny, founder of the Beer Party named for its advocacy of the popular beverage.
He came in fourth place with 8.1 percent, according to the projections.
Alexander Nittmann, 35, a software developer, said he had voted for Wlazny, hoping he would bring "a breath of fresh air".
Van der Bellen -- who supporters affectionately call "the professor" -- faced an unexpectedly tough fight in 2016, only winning the race in a run-off against an FPOe politician.
But the FPOe's ratings have plummeted since 2019 after a corruption scandal brought down the government they were part of and eventually led to the resignation of then-chancellor Sebastian Kurz himself in 2021.
Ahead of Sunday's vote, analyst Thomas Hofer said it is "crucial" that Van der Bellen avoids a run-off like in 2016 when the campaign was "very divisive and hostile".
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Trademark professorial manner
"Van der Bellen stands for integrity and stability, which is very appreciated by voters given the multitude of crises that many European countries are currently facing," Julia Partheymueller, a political analyst at the University of Vienna, told AFP.
Known for his trademark professorial manner, Van der Bellen will be Austria's oldest head of state to be sworn in if he wins.
The presidential post, with a term of six years, is largely ceremonial.
Van der Bellen -- also known as "Sasha", a nickname that nods to his Russian roots -- was born during World War II in Vienna to an aristocratic Russian father and an Estonian mother who fled Stalinism.
The arrival of the Red Army a year later forced the family to escape to the southern state of Tyrol, where Van der Bellen spent an "idyllic childhood".
He studied economics at the University of Innsbruck and finished his PhD in 1970 before going on to become dean of economics at the University of Vienna.
At an election event last month, Alexandra Hoefenstock said she would vote Van der Bellen as he had managed the political crises well in his last stint in office.
"I hope for political stability," the 38-year-old Vienna city worker said.
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