Lidia Thorpe will now make history as the first Indigenous woman elected to the Victorian Parliament.

The Greens will hold three lower house seats in Victoria, extending their reach in Melbourne's inner suburbs.

The party's volunteers and staff members danced, embraced and cheered at the Thornbury after-party as the results rolled in.

Ms Thorpe took to the stage amid thunderous chanting and applause.

"We said we'd make history and we did," she said.

The victorious candidate also paid respect to Fiona Richardson, whose death in August created the vacancy in the seat.

Ms Thorpe said she had received messages of support from Aboriginal people throughout Australia.

"Little old Northcote has hit the map across the country."

"For a kid that left school at 14 I just want to send a message to every kid out there that anything is possible."

Victorian Greens Leader Samantha Ratnam told an ecstatic crowd Ms Thorpe had secured almost 60 per cent of the two-party preferred vote.

"Tonight the people of Northcote have sent the strongest and most powerful of messages," Ms Ratnam said.

Counting showed huge swings toward the Greens' Lidia Thorpe, who won 56 per cent of the primary vote by 8.30pm putting her on course for a decisive victory over Labor's Clare Burns.

The first results from the Darebin, Bell and Alphington booths saw the Greens surge out to an strong lead and Labor campaigners looking nervous.

After the polls closed at 6pm campaign workers, gathering at the after parties, were predicting the vote would be decided by preferences with little to separate Ms Burns from Greens challenger Lidia Thorpe.

But it soon became clear that the Greens surge was strong. The mood became morose at Labor's after party compared to a very upbeat Greens function.

Labor has held Northcote, which was left vacant by the death of government minister Fiona Richardson in August, since 1927 and has campaigned fiercely to defend its turf.

At 7pm Ms Thorpe said she was unsure which way the result would go but felt the mood on the booths had been positive throughout the day.

She said many voters had told her they'd supported Labor their entire lives but this election they were switching to the Greens.

Ms Thorpe said she was confident the seat would eventually turn Green regardless of the weekend's result.

"I have no doubt about that," she said. "We'll keep the pressure on. Labor knows this is going to turn Green eventually."

At Labor's after-party at the Thornbury Theatre the mood was tense as volunteers, supporters state MPs and ministers gathered to dry off after Saturday afternoon's soaking.

Labor has gradually ceded ground to the Greens in Northcote in recent state elections, holding the seat by 6 per cent until Saturday's by-election.

Its campaign honed in heavily on housing affordability and renters' rights – spruiking Ms Burns' residence in a Northcote share house at every opportunity.

Labor also expected a string of socially progressive policies, including creating a supervised drug injecting room and spending millions of dollars on local schools would help retain the electorate.

Meanwhile, the Greens promoted Ms Thorpe's Aboriginal heritage urging voters to elect the first Indigenous woman to the Victorian Parliament.

The smaller party also sought to wedge Labor on its failure to create the Great Forest National Park, east of Melbourne, so far this term.

Labor insiders believe that retaining Northcote would boost the party's chances of defending Richmond which it holds by 1.9 per cent and Brunswick on 2.2 per cent – both against the Greens at 2018 election.

Labor outmanoeuvred its rival on preferences, stitching up a deal with the Animal Justice Party and libertarian outfit the Liberal Democrats.

A total of 12 candidates contested the election, including the Reason Party's Laura Chipp, daughter of Australian Democrats founder Don Chipp and former Darebin mayor Vince Fontana who ran as an independent.

The Greens already hold two lower house seats, Melbourne and Prahran, in the Victorian Parliament and five upper house seats.