Mr Pesutto lost the Federal Court battle on Thursday, with Justice David O'Callaghan ruling he did defame former Liberal MP Moira Deeming by implying she was associated with Nazis.
Mr Pesutto made the defamatory comments in media interviews and a party expulsion motion following a March 2023 rally Mrs Deeming attended.
He said the ruling was disappointing but he would not step down as Liberal leader.
"I've always been a fighter and I've always been a fighter for the right reasons and for the right people - the Victorian people," he told reporters on Thursday afternoon.
"That's why I will continue in this role now, more than ever."
Mrs Deeming launched the legal action in December 2023, claiming Mr Pesutto defamed her by suggesting or implying she was a Nazi or Nazi sympathiser following the Let Women Speak rally.
Moira Deeming has been awarded $300,000 in damages. (Joel Carrett/AAP PHOTOS)
The trans-critical event in March 2023, which Mrs Deeming addressed and helped organise, was attended by men in black who performed the Nazi salute on the steps of state parliament.
Justice O'Callaghan found Mr Pesutto defamed Mrs Deeming in a media release, two radio interviews, a press conference and in a party expulsion motion following the rally.
Mr Pesutto implied she was unfit to be in the parliamentary Liberal Party because she was associated with Nazis.
He also implied Mrs Deeming participated in the rally and knowingly worked with other organisers to help promote a Nazi agenda and white supremacist views, Justice O'Callaghan found.
"The imputations that I have found to have been carried are very serious ones," he said in his judgment.
"They were inherently likely, using mass media to communicate a message to the general public in Victoria, to cause serious harm to Mrs Deeming's reputation."
Justice O'Callaghan determined Mr Pesutto's defences of public interest, honest opinion and qualified privilege had failed.
He also rejected Mr Pesutto's submissions that Mrs Deeming already had a bad reputation prior to the rally.
"The evidence established that she, like all politicians, has her detractors on the other 'side' of politics," the judgment said.
"That may be a reflection of what nowadays passes for political debate, but it is not ... evidence of the fact that Mrs Deeming has hateful views or gives succour to them."
Moira Deeming said she'd push to be let back into the Liberal Party after being unjustly expelled. (Joel Carrett/AAP PHOTOS)
The judge ordered $300,000 in damages be awarded to Mrs Deeming.
Mr Pesutto was not in court to hear the decision, while Mrs Deeming was supported by her husband and a group of women who cheered after the judge left the bench.
Mrs Deeming, who was expelled from the Liberals in May 2023, said the ruling was "cathartic" and she would now push to be let back into the party.
"I was unjustly expelled," she told reporters.
"I have every right to be there. All the accusations that were made about me - they were just disproven in court."
John Pesutto said he was unaware of any sentiment to topple him. (Joel Carrett/AAP PHOTOS)
Mr Pesutto said it would be up to party members to decide whether Mrs Deeming was allowed back in.
"Re-admission to the party is available for anybody who wishes to invoke it and I've never stopped anyone from bringing such matters to the partyroom," he told reporters.
He was also confident his role as leader remained tenable and he would not be toppled.
"What members wish to do is entirely their prerogative but I'm not aware of any such sentiment," Mr Pesutto said.
He said his lawyers would review the judgment before deciding whether to appeal.
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