Gay conversion therapy is "bigoted quackery" and it will be banned in Victoria, Premier Daniel Andrews has announced at a pride march in Melbourne.

The state government says the ban would be an Australian first and comes after an investigation by the Health Complaints Commission the practice resulted in long-term psychological harm and distress.

The so-called therapy has changed and even cost people their lives, Mr Andrews said before joining the Midsumma Pride March in St Kilda on Sunday.

Premier Daniel Andrews (centre) is seen during the Midsumma Pride March. (AAP)

"This bigoted quackery that masquerades as healthcare, the notion that any gay Victorian is broken and needs to be fixed ... that's such a hurtful, wrong and frankly an absolutely disgraceful way to approach what should be about inclusion and acceptance and valuing people just for who they are," he said.

It'll be a year at least before legislation is introduced to parliament, allowing for consultation and to ensure the laws are exactly right, Equality Minister Martin Foley said.

"The Health Complaints Commission's report points to some deep-seated, well-entrenched practices here," he said.

"We want to make sure we don't push those practices to the fringe of society and underground, so getting this right is actually quite the complex process."

Attendees of the Midsumma Pride March are seen along Fitzroy street in St Kilda, Melbourne today. (AAP)

Liberal MP David Davis told reporters at the march that the state opposition in principle supported the move but was waiting for more detail.

"We've obviously not been supportive of this approach by a number of individuals but clearly, we'll await the final legislation," he said.

Independent federal MP Kerryn Phelps, who is in a same-sex relationship, wants the rest of the nation to follow suit.

"It should be banned nationally. I would like to see Scott Morrison as the prime minister step-up," she told reporters on Sunday.

The proposed legislation is expected to include a mix of civil and criminal laws and educative measures, to be determined through extensive and respectful consultation with communities including LGBTI people and faith-based organisations.