Warren Pickering sensationally admitted on Tuesday to taking speed, ecstasy and marijuana in his 20s and losing his licence three times for "low level" drink driving at age 18, 20 and about a decade later.
The former combat engineer's admissions, made when flanked by his daughter and stepson, came after The Australian newspaper published a series of allegations raised by his former partner of almost 20 years, Jo Scott.
Mr Pickering, who is standing for the lower house seat of Pakenham in the November state election, denied ever being a drug addict or using ice, also known as crystal methamphetamine, while their children were home.
A handwritten note from Mr Pickering referring to "sexual deviance" related to behaviour after the couple opened their relationship to a third person at a time when Mr Pickering was "exploring his own sexuality", One Nation's national director James Ashby said.
In a lengthy social media post on Wednesday, Senator Pauline Hanson described it as a story of personal redemption.
"Warren's story shows a man who confronted his mistakes, changed the direction of his life and chose not to remain defined by the worst decisions of his youth," the federal leader of One Nation wrote.
Federal One Nation MP Barnaby Joyce commended Mr Pickering for correcting the record after the 43-year-old previously rejected all of Ms Scott's claims.
"If people turn their life around, you can either pat them on the back as an example of what everybody should do (or) you can kick them in the knee," Mr Joyce told reporters in Canberra on Wednesday.
"I'm not in the group to want to kick some in the knees."
Victorian One Nation MP Rikkie-Lee Tyrrell said Mr Pickering had previously disclosed elements of his past to her, including drug use.
She backed him remaining the state party leader and believes coming clean might resonate with the public.
"It shows that we are real people," Ms Tyrrell told reporters at state parliament.
Political analyst Kevin Bonham pointed out One Nation recently triumphed over Labor in a by-election for the WA seat of Secret Harbour despite candidate Luke Herdegen admitting to drug use.
"The stuff that came out about Pickering under normal circumstances would destroy a major party candidate but this is not normal anymore," he told AAP.
"The things that are driving people to One Nation may cause a lot of them to say 'who cares'.
"It's similar to how Trump voters will forgive Trump for absolutely everything. They're determined to reject the major parties."
Mr Pickering found an unlikely ally in Legalise Cannabis MP David Ettershank, who said it was very disturbing to witness him being stigmatised and criminalised.
Victorian Alcohol and Drug Association acting chief executive Scott Drummond said he was optimistic these sort of conversations helped to reduce stigma for others.
"The more we can talk about these topics in adult, nuanced ways, bringing compassion and understanding instead of judgment and discrimination, the better," he said.
Deputy Premier Gabrielle Williams said people deserved an opportunity to rebuild their lives but described some of allegations against Mr Pickering as "very serious".
One Nation has promised to get tough on crime in Victoria and any visa holder who breaks the law would be deported under the federal party's immigration platform.
The leader of the Victorian Greens, Ellen Sandell, suggested the strict stance, in light of Mr Pickering's admissions, highlighted One Nation's hypocrisy.
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