The Australian Labor Party's ACT branch has voted overwhelmingly in support of same-sex marriage.

A small group of activists gathered outside the ALP's ACT branch conference in Canberra on Saturday, calling for a decision supporting same-sex marriage.

They chanted: "One, two, three four, equal rights before the law."

Inside the building, delegates passed a motion that calls on Labor's national conference in December to support the right of all couples to be married, regardless of gender or sexual orientation.

The ACT's deputy chief minister, Andrew Barr, is openly gay and says it is time for change.

"I think there's momentum building across state and territory branches, across all factions," he said.

He says ACT delegates have also rejected a civil union scheme as a compromise

"What the ACT branch has done today is taken a very strong stand on the issue of equal marriage," he said.

"We've taken a position as an ACT branch in support of removing discrimination from the Commonwealth Marriage Act.

"We've also indicated support for that debate to be had at the party's national conference."

All state and territory branches of the ALP have passed similar motions, except New South Wales, which referred the issue to the party's national conference.