The milestone comes more than two years after former health minister Meegan Fitzharris announced the government's intention to ban the practice, which she described as "abhorrent and completely inconsistent with the values of Canberrans".

Under the proposed legislation, people would face fines of up to $24,000 and 12 months' imprisonment for performing a "sexuality or gender identity conversion therapy" on a child or individual with an impaired decision-making ability.

An offence would be committed regardless of whether the individual or their parent or guardian consented to the practice.

The same penalties would apply for taking a child or vulnerable person out of the ACT for the purpose of performing the practice.

Chief Minister Andrew Barr last year indicated that the process of establishing a legal definition of conversion practice was the reason it had taken so long for laws to be drafted and presented to the Legislative Assembly.

The bill presented on Thursday defined it as a treatment or practice which was aimed at changing a person's sexuality or gender identity.

However, it does not cover practices related to supporting a person who is undergoing or considering a gender transition.

The legislation would not prohibit practices which help a person express their "gender identity" or that person's "coping skills, social support or identity exploration and development".

A coalition of religion-based education organisations and schools raised concerns about the proposed ban earlier this year, after it emerged the ACT government had dispensed with public consultation on a preferred model because of the COVID-19 pandemic.

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Instead, the government sought direct feedback from selected stakeholders, including religious groups, medical experts and gay conversion therapy survivors.

In their submission to the Barr government, Christian Schools Australia, Adventist Schools Australia, the Australian Association of Christian Schools and the Islamic School of Canberra sought a guarantee that the rights of religious organisations and parents to continue teaching in line with their beliefs about gender and sexuality were upheld.

On Thursday, Mr Barr said the legislation was not about banning religious expression.

"This bill is about protecting vulnerable people from harm," he said.

"Religious individuals and institutions will still be able to teach their faith and provide guidance as to how to abide by religious tenets. They will only be prohibited from carrying out those practices directly targeted at changing an individual's sexuality or gender identity."

The ACT Human Rights Commission would assess complaints about conversion practices, under the government's legislation.

"The ACT government wants to send a clear message that sexuality and gender identity conversion practices are not tolerated in our society," Mr Barr said.

"Too often in Australia, we hear horrific stories of young people being coerced into co-ordinated and unregulated programs that seek to change their gender identity or sexuality."

Justice Minister Shane Rattenbury, who co-sponsored the bill presented on Thursday, said the practice was abhorrent, dangerous and outdated.

"They can lead to anxiety, depression, substance abuse, even suicide. Survivors say it can take a whole lifetime to undo the damage caused - if achieved at all," he said.

"Transphobia and homophobia in all their forms have no place in Canberra."