New same-sex marriage laws will be put to the ACT parliament this week but constitutional experts warn the legislation may not supersede commonwealth laws.
The territory's minority Labor government will present its Marriage Equality Bill to the Legislative Assembly on Thursday.
The legislation applies to people - that is, same-sex couples - who can't legally wed under the commonwealth Marriage Act.
Attorney-General Simon Corbell believes the ACT laws can withstand a High Court challenge because the commonwealth act defines marriage as between a man and a woman.
This means there's space for states and territories to legislate to allow same-sex couples to wed because the federal law wouldn't apply to them, he argues.
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Mr Corbell also points to legal advice provided to the ACT government in 2008, relating to its 2006 same-sex civil unions bill, supporting this stance.
"The same legal principles apply and that's why we've made that opinion public," he told AAP on Monday.
"But we have also undertaken further analysis by the ACT Solicitor-General in coming to our decision."
University of Sydney constitutional law expert Helen Irving says the stronger argument is that the commonwealth law is intended to cover all kinds of marriage.
"When you have an act called the Marriage Act and it defines marriage as a certain type of union, that's what marriage legally means," she told AAP.
"It's not an act that's called the Heterosexual Marriage Act, which allows there to be the Same Sex Marriage Act and other types of marriage conceivably."
While Professor Irving would be happy to see same-sex marriage laws, she didn't believe it could happen unless the federal law was also changed.
There was also a risk federal parliament could vote to overturn the ACT laws.
Australian Greens senator Sarah Hanson-Young said the minor party would fight any attempt by the current federal coalition government to do this.
Mr Corbell welcomed the Greens' support.
"Equally, I would expect there to be support from my federal (Labor) colleagues in the Senate," he said.
Legalising same-sex marriage could lead to a wedding industry boom in the ACT, although Mr Corbell was quick to say that wasn't the government's primary motivation in drafting the laws.
"It would only serve to highlight further that there is the demand for law reform in this area right across the country," he said.
The ACT same-sex marriage laws fulfil a Labor election promise and an agreement with the Australian Greens under which Greens MLA Shane Rattenbury supported the party to government in the ACT.
