Would-be voters have one week to enrol in the seat left vacant by the death of Labor's Fiona Richardson, with the electoral roll closing next Thursday.

Political hopefuls must declare their candidacy by October 19, State Parliament confirmed on Thursday.

The two main contenders have already entered the ring, with the Greens' Lidia Thorpe, to take on Labor hopeful and Trades Hall official Clare Burns in a dress rehearsal for the broader struggle in inner-Melbourne seats at next year's state election.

A Greens win in Northcote, or even a narrow loss, would make Labor's defence of its other threatened inner-city seats of Brunswick and Richmond in next year's state election, look like a lost cause.

But a comfortable Labor victory would give Daniel Andrews' troops a massive confidence boost, 12 months out from the November 2018 state poll.

Ms Richardson held Northcote with a margin of 6 per cent, making it still a notionally safe Labor seat.

But the Greens are hoping the influx of younger, wealthier, Greens-leaning voters, replacing Labor's older working-class cohort, would tip the contest in their direction.

The ALP was quick out of the blocks with Premier Daniel Andrews joining the party's candidate at Northcote Primary School last week to announce more than $3 million for long-needed repairs while the Labor machine launched a billboard campaign around the seat.

But Greens strategists say their strength in the contest will be their on-the-ground volunteer campaign, claiming their "green shirts" will easily outnumber, and out-doorknock Labor's campaign workers.

Ms Thorpe told Fairfax on Thursday that the two-month campaign period played to the Green's strengths.

"The longer time we have, the more time we have in the community and that's one of the great strengths of our party," she said.

"We're gaining more and more support each day."

The candidate shrugged off her party's recent woes at the federal level.

"We've got a strong connection with our community so that won't come into it at all," she said.

Ms Burns said she was excited that a date had been set for the by-election.

"I hit the ground running once I was pre-selected, but I'm so excited that the campaign has now kicked off in earnest," the Labor candidate said.

"I will be working hard for every single vote and campaigning to give the people living in Northcote a fair crack at the housing market, whether that's renting or owning their own home."

The Victorian Electoral Commission confirmed there are now 48,000 voters registered in Northcote, a big 8.5 per cent increase on the 44,000 who were enrolled when the seat last voted in the 2014 state election.

More than 1200 of the new voters have added their names to the rolls since the Turnbull government's same-sex marriage postal survey was announced in August.