Jacinta Allan is refusing to step down after a cross-factional delegation, including six ministers, informed the embattled premier she had lost majority support of the caucus.
A leadership spill motion is expected to be put to the caucus on Tuesday morning which, if successful, would open the floor to a leadership challenge just four months out from the election.
The besieged premier, from the party's left faction, has flagged her intention to nominate for the leadership if it goes to an internal vote.
Deputy Premier Ben Carroll, from the party's smaller right faction, has confirmed he will throw his hat into the ring.
If the leadership challenge eventuates, caucus and rank-and-file party members will vote for their preferred leader in a weeks-long process.
A caretaker premier, who is not a nominee, would need to step in to lead the party during that time.
But shadow attorney-general James Newbury said a change of government, not leadership, was needed.
"Changing the leader will not change the problems that Victorians face," he told reporters on Monday.
"Victorians don't need another premier who hasn't been elected - what Victorians need is an election."
He described Mr Carroll as Ms Allan's "partner in crime," and called on Labor MPs to back a parliamentary no confidence motion in the premier's leadership scheduled for Tuesday afternoon.
There's "absolutely no guarantee" Mr Carroll could lead Labor to a record fourth-straight victory if he were to become premier, Redbridge pollster and former Liberal strategist Tony Barry said.
A significant cabinet reshuffle and policy overhaul would be needed to differentiate Mr Carroll's politics from Ms Allan's and subsequently remedy the drop in voter support incurred under her leadership, Mr Barry said.
"There's going to have be changes around the Suburban Rail Loop and other things where he differentiates himself from Jacinta Allan," he said.
"Otherwise he's going to be completely open to the attack of same horse, different jockey.
"In that situation, he might make a bad situation even worse."
Labor's push to put the leadership to a vote has dealt Ms Allan's chances of leading the party at the election "a mortal blow", Mr Barry said.
"They have probably done her irrecoverable damage in the last 24 hours which makes her position untenable," he said.
Support for Labor has been diminishing in the polls since the last election, with fresh Newspoll figures from The Australian indicating the party's primary vote is trailing the Victorian coalition on a two-party-preferred basis 52 per cent to 48 per cent.
Ms Allan has faced mounting pressure in recent months following revelations of corruption on Big Build projects.
She has refused to call a royal commission into the sector after corruption-busting lawyer Geoffrey Watson estimated it had cost the state $15 billion.
Persistent crime and a failure to reach a pay deal with public school teachers have also dogged the government.
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