Sam Hibbins, the MP for Prahran, announced he was resigning from the Greens and will sit as an independent on Friday after having a "consensual relationship with a staff member, which breached party rules".
Party leader Ellen Sandell said she had received a complaint on Tuesday about her co-deputy and after meeting with him, said some allegations were confirmed while others were contested.
The staff member involved was "very distressed" and Ms Sandell said the party was doing all it can to support them.
The Greens leader expressed her anger and said Mr Hibbins did not meet the standards of behaviour and expectations of an MP, falling short of calling on him to resign from parliament.
Sam Hibbins wouldn't be welcome back in the Greens party room, leader Ellen Sandell said. (James Ross/AAP PHOTOS)
"He is no longer a member of our party room, and he will never be welcomed back as a member for our party room," Ms Sandell said.
Mr Hibbins, who is married with two children, said he was aware his announcement was a distraction from his work with the Greens but would "remain committed to serving (his) electorate of Prahran".
"I accept the consequences of my decisions," he said.
"I am working to make amends to the most important people in my life, my family and our community."
It is not the first time this parliamentary term has seen controversy after Premier Jacinta Allan dumped two Labor MPs, Will Fowles and Darren Cheeseman, for past instances of alleged misconduct.
Former Victorian Greens leader Greg Barber had allegations of sexism levelled against him over his time in parliament, including claims he had a "men's room" in his office, according to the ABC.
Mr Barber previously said he could not comment on the claims, even to defend himself, as he had been committed to confidentiality as apart of a legal settlement.
The NSW Greens were embroiled bullying allegations in 2018 after former MP Jeremy Buckingham, now upper house member for Legalise Cannabis, alleged party members were bullied into asking him to resign.
He had been the subject of a 2011 sexual harassment allegation re-aired under parliamentary privilege by factional rival Jenny Leong, although an independent investigation recommended no adverse findings against him and he had denied the alleged incident.
ACT Greens backbencher Johnathan Davis resigned from the party and the parliament in 2023 after he was stood down over sexual misconduct allegations.
He has not been charged and has had no formal finding made by any authorities.
West Australian Greens Senator Dorinda Cox in October apologised for shortcomings following allegations of bullying after after 20 staffers had left her office in three years.
But the senator said there was a "disappointingly significant missing context" around the situation.