Mr Hofer, 45, won last month's first round but failed to avoid the run-off.
If he wins on Sunday, Mr Hofer could become the EU's first far-right head of state, although Austria's president plays a largely ceremonial role.
On Thursday, the two rivals traded accusations during a TV debate.
Mr Van der Bellen, 72, accused Mr Hofer of wanting to dismiss any government that did not suit him.
He was referring to the fact that, despite limited powers, the president can sack governments and also swears in chancellors.
Mr Hofer countered that Mr Van der Bellen was the one who had refused to swear in a Freedom Party chancellor if the party won at the next general election in 2018.
However, the debate was said to be less feisty than last Sunday's TV encounter, described by some commentators as a slugfest.
In the first round of voting, Mr Hofer secured 35% of the votes, while Mr Van der Bellen, polled 21%.
For the first time since World War Two, the candidates from Austria's two main parties - the Social Democrats and the People's Party - did not make it to the run-off.
Both parties have governed Austria for decades - either alone or in coalition.
This is a big shake-up in Austrian politics, as the country has had a president from the centre-left or centre-right since 1945.
The victory in the first round of the far-right candidate reflects widespread discontent with the status quo, as well as concerns about immigration and the economy, correspondents say.
Support for the Social Democrats and the People's Party has been falling in recent years.
In the last general election in 2013, the two parties won just enough votes to govern in a "grand coalition".
Incumbent President Heinz Fischer, 77, cannot run again after two terms in office.
Austria's far-right Freedom Party presidential candidate Norbert Hofer and his rival, Green-backed Alexander Van der Bellen, are holding final rallies ahead of a run-off vote.