From Thursday, anyone in Victoria who makes another person change or suppress their sexual orientation or gender identity can face criminal charges and potential jail time.
Victorian Attorney-General Jaclyn Symes described the now-illegal practices as "total quackery".
"These laws send the clear message that these disgraceful practices are not tolerated in Victoria," Ms Symes said. "We'll always have the LGBTIQ+ community's back - now the law does too."
Minus18, an organisation advocating for LGBTIQ+ youth, has welcomed the reforms.
"Coming to accept sexuality or gender identity is an incredibly delicate time in anyone's life, particularly for a young person who is seeking help from a professional," founding chief executive Micah Scott said.
"We are in touch with countless young people at Minus18 who have been subjected to suppressive practices from a professional that caused them to believe their sexuality or gender identity is wrong and needs to be fixed.
"The shame and mental harm caused by this is deep and long lasting."
Mr Scott said the new laws gave young people and their families the confidence to engage in professional support, knowing the services had their best interests at heart.
Transgender Victoria chief executive Mama Alto said wide-ranging research from the Human Rights Law Centre and La Trobe University showed the harm the practices caused.
"Now that these practices are unlawful ... trans, gender diverse, and non-binary Victorians can be protected from these harms and experience better mental health outcomes," she said.
"The message is clear: we are not wrong, we are not broken, and we are as equally human as anybody else."
The Victorian parliament passed the conversion therapy reform in 2021 after working with survivors.
The reforms will empower the Victorian Equal Opportunity and Human Rights Commission to accept and act on reports of change or suppression practices.
The commission's civil response scheme will support survivors, address the harm they have endured, and educate the public about the ban.
It will also be able to launch investigations where there is evidence of serious or systemic change or suppression practices.
It comes after the New Zealand parliament on Wednesday passed a law to ban conversion practices.
Under the legislation, it will be illegal to perform conversion practices on a child or young person aged under 18, or on someone with impaired decision-making capacity.
It will also be an offence to perform conversion practices on anyone - irrespective of age - where the practices have caused serious harm.
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