He will have earned some new friends among other EU leaders too after Sunday's ballot re-run, in which he blocked Freedom Party rival Norbert Hofer from becoming Europe's only far-right head of state.
But it has not all been plain sailing. Van der Bellen — also known as “Sascha”, a nickname that nods to his Russian roots — was decried by critics as a “green dictator”.
The former Greens party leader, who ran as an independent, struggled to convince many conservative voters who accused him of pandering to the left.
Hofer seized upon the sentiment and repeatedly denounced his adversary as a “communist” or even a Cold War spy for the Soviet Union — claims Van der Bellen dismissed as “ridiculous”.
Back in May, the pro-European liberal nonetheless managed to beat Hofer by a paper-thin margin in the run-off, which was then annulled over procedural irregularities.
At 72, the grey-haired economics professor often cut a wooden and somewhat dishevelled figure next to the smooth-talking gun enthusiast Hofer, 45.
If “Hofer is the offensive attacker who knows he can only score if he's not too aggressive, Van der Bellen comes across as a nice, older gentleman,” political expert Peter Hajek said.
This has been Van der Bellen's main selling point to try and sway undecided Austrians.
Van der Bellen 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.
Van der Bellen's trademark professorial manner has often riled Hofer.
“I'm talking about Europe: E-U-R-O-P-E. Never heard of it?” Van der Bellen taunted his opponent during a TV duel.
“My God, the schoolmasterliness, Herr Doctor Van der Bellen,” an agitated Hofer shot back.
Controversially, Van der Bellen vowed not to swear in FPOe chairman Heinz-Christian Strache as chancellor if the poll-leading party wins the next general election scheduled for 2018.
The remark, which Van der Bellen later rowed back on, prompted Hofer to call him a “green dictator”.
Not smoking is 'torture'
Critics have also accused Van der Bellen of being a “turncoat” because he was a member of the Social Democrats before joining the Greens in the early 1990s and eventually becoming their president.
Under his leadership, the Greens went on to achieve record results, but he quit after the 2008 election when the party lost votes for the first time in almost 10 years.
“I have made my way from being an arrogant anti-capitalist to a generous left liberal”, he once said.
As Austrian president, he dreams of a fence-free “United States of Europe”.
An outspoken supporter of gay marriage, the divorced and recently remarried father-of-two has received strong backing from celebrities, artists and the country's top politicians.
Despite his austere appearance, he has also many young fans who organised big dance raves in his support.
Van der Bellen will be Austria's second-oldest head of state at the time of his election.
His age, combined with a heavy smoking habit, have repeatedly raised questions about his health.
In late August, Van der Bellen was forced to dispel cancer rumours by releasing his medical records proving he had “wonderful lungs”.
He insisted he had no intention of giving up smoking. “I once quit for four months… but why should I torture myself at my age!” he said.