The independent ecologist is running against Norbert Hofer who is striving to become the EU's first far-right elected head of state on December 4th. Opinion polls suggest the race is too close to call.
Trump's triumph is "a wake-up call, not just for December 4 but beyond," Van der Bellen, 72, told a news conference in Vienna. "I don't want Austria to become the first western European nation where right-wing demagogues take power."
Like Trump and other populist groups in Europe, Hofer's Freedom Party (FPÖ) has boosted support by stoking concerns about immigration and what it portrays as an out-of-touch elite.
The FPÖ is consistently topping opinion polls ahead of the next scheduled general elections due in 2018 -- if Chancellor Christian Kern's unloved and fractious "grand coalition" lasts until then.
For the presidency, Van der Bellen narrowly beat Hofer in May but the FPÖ got the result overturned due to procedural errors. A re-run set for October was postponed to December because of faulty glue on postal vote envelopes.
The largely ceremonial role of Austrian president still carries considerable cachet, and a victory for Hofer would likely be a major boost to the far-right both in Austria and further afield.
The softly-spoken Hofer, 45, told the Kurier newspaper in an interview published on Wednesday that he does not see any correlation between the US and the Austrian elections. "Except: it shows that sooner or later elites who don't concern themselves with the people will be voted out of office by them," he said.
He added that his "statesmanlike neutrality" over the US election "was better than Alexander Van der Bellen with his wild insults against Trump."