Australia's dominant party has voted to endorse gay marriage.

At its annual conference in Sydney, the Australian Labor Party (ALP) agreed to alter its long-standing party platform on the issue.

But the impact of the vote was diluted when the party also endorsed Prime Minister Julia Gillard's motion to allow lawmakers to make a “conscience vote” on bills related to gay marriage, which allows lawmakers to vote as they please rather than the party line.

Despite that setback, gay marriage proponents praised the move.

“The momentum toward achieving marriage equality is unstoppable,” Australian Marriage Equality national convener Alex Greenwich told the AP. “A major obstacle to reform has been removed and we are prepared to face the new challenge we have been given of achieving reform with a Labor conscience vote.”

Lobbying for the change were ACT Deputy Chief Minister Andrew Barr and Finance Minister Penny Wong.

“I can see no good argument for allowing only opposite sex couples to formalize and celebrate their relationships through marriage and to deny that to same-sex couples,” Barr told conference attendees.

“If instead lesser rights were proposed on the basis of race or age or class or any other attribute there would not be a person in this hall who would countenance it,” Wong said.

Within hours of the vote, Labor backbencher Stephen Jones announced he would introduce a private members bill to legalize gay marriage in Australia.