Attorney-General Simon Corbell was one of a number of speakers who addressed the Equal Love rally, with an estimated 120 people marching down Bunda Street and through the Canberra Centre on Saturday afternoon.

The rally came as News Corp reported Mr Corbell's federal counterpart, George Brandis, had received advice from the Commonwealth Solicitor-General indicating the ACT laws were unconstitutional because of their inconsistency with the federal Marriage Act.

The advice could encourage the Abbott government to challenge the laws in the High Court rather than override them through a bill in Parliament.

Equal Love Canberra spokesman Chris Bourne said he was happy with the size of Saturday's turnout, with the rally largely focused on support for the territory bill, but also calling for a federal change.

"I'm supportive of every potential measure that reduces discrimination, and even though the ACT bill is not ideal - in that it doesn't help people from Victoria, for example - we support it," Mr Bourne said.

"It's nice to see we're having good-sized numbers, because we're going to need numbers to respond to Tony Abbott's attack when it does happen."

Mr Bourne, 23, said Mr Corbell told the crowd the ACT bill would stand up to a court challenge, with the Labor minister later tweeting the law could operate concurrently with the federal act.

The former Downer resident, now living in Wollongong, said the introduction of same-sex marriage laws was in part symbolic, but an important move.

"Even though civil unions offer practically nearly identical rights, they're still different [to marriage]," Mr Bourne said.