Australia's capital allows gay marriage

Same-sex unions are available in a majority of Australian states but because marriage comes under federal legislation these couples are not formally recognised as married by the government.

The new law passed by the Australian Capital Territory's (ACT) 17-member Legislative Assembly in Canberra means the first weddings could take place by the end of the year, Chief Minister Katy Gallagher said.

"I am sorry that the Commonwealth threat hangs over this law," Gallagher said referring to the national government's warning it would challenge the law in the High Court. "But couples who marry will do so with their eyes open to the action that the Commonwealth is taking."

She added: "We understand this creates some uncertainty ahead, but that should not deter us; it does not rattle us and it doesn't change our path."

The Marriage Equality Act means that gay couples from outside the small ACT, home to the city of Canberra and the national parliament, could travel there to be wed by an authorised celebrant.

Gallagher said national Attorney-General George Brandis had urged her not to go ahead with the legislation as it was inconsistent with federal laws that do not permit same-sex weddings.

Brandis has vowed to challenge the move in the High Court, with the outcome potentially affecting those who used the law to wed.

"It would be very distressing to individuals who may enter into a ceremony of marriage under the new ACT law, and to their families, to find that their marriages were invalid," he said earlier this month.

Gallagher said activists had fought too hard for too long to be put off by another legal hurdle, adding that the ACT was confident its law was strong.

"We are simply legislating to improve outdated, inhumane laws," she said.

Gallagher acknowledged opposition to the change, particularly from those of strong religious faith, but said the bill did not in her view challenge, diminish or undermine the religion or faith of any individual.

"If we are to be judged by a higher being on this law then let it be so," she said.

ACT opposition leader Jeremy Hanson opposed the bill which was passed with the support of Greens member Shane Rattenbury after some emotional debate.

"We do not see the ACT Assembly as a vehicle to drive national agendas on social agendas," Hanson said.

"We are Australia's smallest parliament in a small jurisdiction and we do not think that a majority of one person in the ACT should change the definition of marriage for a country of over 23 million people."

Gay marriage has recently been a high-profile political issue in Australia, home to one of the world's largest annual gay and lesbian mardi gras celebrations in Sydney.

Federal parliament last year voted down laws allowing same-sex marriage when conservative members opposed the move as a block after leader Tony Abbott denied them a conscience vote on the sensitive issue.

Abbott, who does not support gay marriage, has since become Prime Minister but so far has not heeded the urgings of his gay sister Christine Forster who has called for MPs to be allowed to vote as their conscience, not the party, dictates.

"Marriage is about love, it's about people's feelings, it's a matter of the heart," Forster told Channel Nine on Tuesday.

"That for me means it should be a conscience decision, rather than a policy decision."

In April New Zealand became the first Asia-Pacific country to legalise gay marriage.