Jeremy Hanson.

Liberal leader Jeremy Hanson says it is inappropriate for the Assembly to debate marriage equality legislation. Photo: Jay Cronan

Same-sex couples who wed under ACT laws could quickly find their marriages annulled if a High Court challenge was mounted, the ACT opposition has warned.

The ACT government will introduce a bill to the Legislative Assembly to allow same-sex marriages in the territory.

The bill is likely to pass the 17-member Assembly with the support of all eight Labor MLAs and Greens member Shane Rattenbury.

But Liberal leader Jeremy Hanson said it was inappropriate for the Assembly to debate marriage equality legislation.

Mr Hanson said any local same-sex marriage law would inevitably be challenged through the courts because marriage was a matter for the Commonwealth.

''I don't think it's something that we can pass in the Legislative Assembly without it being challenged in the High Court,'' he said.

The ACT government has legal advice that the Assembly can legislate for same-sex marriage without coming into conflict with the federal Marriage Act.

But some legal experts believe state or territory-based same-sex marriage laws could be struck down by the High Court.

Mr Hanson said the eight Liberals in the Assembly had differing views on same-sex marriage but all agreed it was an issue that should be resolved at the federal level.

''Ultimately, I don't think that this is something that we should be driving as a controversial social issue out of the Legislative Assembly of the ACT,'' he said.

''It's a national issue. We just had a federal election and the two parties who were advocating gay marriage went backwards significantly.''

As well as facing hurdles from possible court challenges, an ACT same-sex marriage law could be at risk of being vetoed by the Federal Parliament.

Greens Senator Sarah Hanson-Young said her party would oppose any attempt to override marriage equality in the ACT.

''Tony Abbott needs to listen to the overwhelming support for equality

rather than bowing to pressure from groups like the Australian Christian Lobby,'' Senator Hanson-Young said.

''As a result of the Greens' Self Government Bill, which was passed in the last term of government, marriage equality in the ACT has been Abbott-proofed by forcing any move to overrule territory legislation must be approved by Federal Parliament. The Greens will stand up to any attempts to dismantle equality in the ACT. ''

Former local Liberals leader Zed Seselja, who appears to have won the second ACT Senate seat at the election, refused to comment on how he would vote if an attempt was made to override the same-sex marriage law.

A spokeswoman for Mr Seselja said it was not yet certain he had won the Senate seat so it was premature to speculate on matters that might or might not come before the Senate.

ACT Labor senator Kate Lundy praised the ACT government for introducing the same-sex marriage bill.

''As a proud member of the ALP, it is my belief that all people are entitled to respect, dignity and the opportunity to participate fully in society regardless of their sexuality,'' Senator Lundy said.