A former Victorian upper house MP has resigned from the Greens, saying the party has become too toxic and riddled by megalomania.

Samantha Dunn says "The Greens are distracted by populism, self interest, power, ego, narcissism, megalomania, appealing to narrowcast demographics and virtue signalling while exercising that old war strategy of divide and conquer."

Ms Dunn, who represented Eastern Metropolitan Region from 2014 until last November, posted the savage critique on Facebook on Thursday as she announced her resignation because she could no longer accept the culture in the Greens.

"Aversion to conflict resolution means that tensions fester, no one is ever pulled up for poor behaviours, the behaviours escalate and become legitimised because no one ever says no or stop it or that's inappropriate," she wrote.

While the minor party managed to claim Brunswick from Labor at the November 24 state election, Northcote went back into ALP hands and four upper house MPs including Ms Dunn didn't make it through.

The party's percentage of first preference votes also dropped - in 2018, they garnered 10.71 per cent and 9.25 per cent of the vote in the lower and upper houses respectively.

But state leader Samantha Ratnam claimed "our vote held despite a very strong swing to Labor" in the weeks after the poll.

Ms Dunn attacked the continued trumpeting of success at the election.

"If this is what success looks like then the benchmark is very low," she said.

The party has been hit by internal disharmony for some time including allegations of bullying and sexual misconduct.

Repeat federal candidate Alex Bhathal quit the party in February, after she was accused of bullying during the Batman by-election, and upon leaving said she had lost faith in the Greens' governance and felt bullied out of the party.

Ms Dunn joined the Greens in 2004 and said she would still be an environmental activist despite her resignation.

Victorian Greens co-coveners Colleen Hartland and Willisa Hogarth said in a statement they were disappointed Ms Dunn had left the party.

"Samantha is a committed activist dedicated to saving Victoria's forests and protecting the environment and we wish Samantha well for the future," the statement read.

"As is normal practice, the party is conducting a review into the 2018 state election, and is committed to learning the lessons from that campaign."