"It's about working together to get outcomes for our community," Ms McBain said of Mr Barilaro on Saturday. "I'll continue to do that."

The seat, which is the size of Switzerland, was a bellwether seat for more than four decades until 2013, falling to the government of the day in each election since 1972. Barring a stunning upset victory from federal Nationals candidate Trevor Hicks, Eden-Monaro will elect its first female MP since federation in 1901.

Saturday's byelection is seen as a key litmus test of the public's reception of the federal government's response to the multiple crises that have marked the first half of 2020.

Opposition leader Anthony Albanese is likely to come under some internal pressure if Labor fails to hold onto the seat.

He said on Saturday that a vote-winning margin of 3 per cent could be attributed to the personal popularity of former Labor MP Mike Kelly.

Mr Kelly, who served with the Australian military in East Timor and Iraq, resigned for medical reasons in April.

COVID-19 social distancing restrictions have limited the personal contact of both campaigns, which has been dominated by pre-polling and postal votes, with up to half the electorate voting before election day.

"We know that we haven't been able to doorknock, we haven't been able to have town hall meetings," said Mr Albanese. "It has been a difficult campaign."

A redistribution of the seat has also seen more conservative-leaning booths around the ACT added to the electorate, but Queanbeyan, which is home to up to 40 per cent of voters, has historically swung to Labor. The seat sits on a margin of just 0.85 per cent.

The large number of postal votes means a result is not expected until late on Saturday. If it is close, the candidates may have to wait until Sunday or early next week until a result is declared.

Ms Kotvojs, a farmer with a doctorate in education, has framed her campaign around rebuilding employment in the depleted region through infrastructure boosts and giving voters a voice inside the government.

"After everything we have gone through, particularly after the fires and COVID-19 and the ongoing drought, that is the key thing," Dr Kotvojs said on Saturday.

The Australian Federal Police charged a 32-year-old man on Saturday after he allegedly sent emails purporting to be from the Catholic Church to voters linking Ms McBain to the coronavirus outbreak.

It is the second byelection in two and a half years to be marred by claims of disinformation: the Wentworth byelection in 2018 was also marked by fake emails that suggested then independent candidate Kerryn Phelps had withdrawn from the race after being diagnosed with HIV.

Ms McBain said on Saturday that disinformation was a "blight on our democracy".

"Those things I don’t think have a place in politics at all,” she said.

Photos of how to vote cards at polling booths on Saturday showed Labor had co-opted Nationals branding and colours to urge Nationals voters to put Ms McBain ahead of the Liberal candidate.