He gave no indication of relenting on his opposition to the issue, nor on his ban on Coalition MPs having a conscience vote.

However, the issue will come before Federal Parliament in the new year, with added pressure due to the High Court's ruling that Parliament could legislate on gay marriage.

The Greens reintroduced a bill to the Senate to allow gay marriage, guaranteeing another debate in Parliament.

It would be supported by Labor if it came to a vote next year, but the Coalition would be locked into opposing it unless Mr Abbott allowed a conscience vote by his MPs.

Greens leader Christine Milne criticised the ACT's bill but joined other federal MPs in welcoming the ruling that Federal Parliament could legislate on gay marriage.

Asked if the ACT bill was flawed, Senator Milne said: ''I'm disappointed that the ACT government didn't take the advice of some of the constitutional lawyers who were suggesting some amendments which they thought would have strengthened the case, so yes, I'm disappointed that didn't happen.''

The Greens would not stop their campaign for same-sex marriage to be legalised.

''What the court has decided has made it very clear that the Federal Parliament has the power to legislate for marriage equality,'' she said.

''The court's decision today has been a blow … it is a setback, it's devastating for the people concerned but it is also a clarion call for everyone around the country who supports marriage equality to now put the pressure on the federal government and the Federal Parliament to change it.''

Despite widespread debate on the ruling, Mr Abbott was not asked about the issue in question time and later his office referred the media to the office of Attorney-General George Brandis.

As expected, Senator Brandis welcomed the ruling, which resulted from the federal government's challenge to the ACT bill.

"The basis upon which the decision was reached by their honours was the supremacy of marriage power … of the constitution," he told Parliament.

"As a result, the inconsistent provisions of the ACT legislation were held to be void and of no effect. Irrespective of anyone's views of the desirability or otherwise of same-sex marriage, it is clearly in Australia's interest that there be a nationally consistent marriage law.

"The Commonwealth Marriage Act provides that consistency."

Senator Brandis said members of Parliament should respect the authority of the court. "Even if the decision went the other way, and the Commonwealth's proceedings had been dismissed rather than upheld, my answer would have been the same."

The Greens' Sarah Hanson-Young, who attended several same-sex marriages in Canberra last weekend, said hearts were breaking in Canberra and across the nation.

''We will get this reform done … this is about love, it shouldn't be about politics,'' she said.

She said Coalition MPs should be allowed a conscience vote on the issue next year.

Member for Fraser Andrew Leigh said his heart went out to the ACT couples who have wed. ''I promise them that we will keep on working to change the law,'' he said.

Shadow attorney-general Mark Dreyfus said the court's unanimous decision made clear same-sex marriage was a matter for the national Parliament to decide.

"Importantly the High Court stated that 'marriage' in the Australian constitution includes a marriage between persons of the same sex; this means that the Parliament can legislate for marriage equality,'' he said.

''The Prime Minister needs to give his MPs a conscience vote on this issue so that the national Parliament can decide.

The Human Rights Law Centre's Anna Brown said the decision did at least point to a way forward.

"Fortunately, there is a silver lining - the High Court has confirmed beyond doubt that the Australian constitution allows the Federal Parliament to legislate for marriage equality,"

While the centre previously expressed concerns about the chances of the ACT's laws surviving the Australian government's challenge, Ms Brown said state-based laws such as the proposals in Tasmania and NSW would have a greater chance of surviving a High Court challenge.

"Importantly, as well as confirming that the Federal Parliament can legislate for same-sex marriage, the problems in the ACT law identified by the court have not been included in the NSW and Tasmania same-sex marriage bills, so there are still ample avenues for Australians to pursue marriage equality," she said.

A statement issued by Labor's ACT federal representatives - Kate Lundy, Gai Brodtmann and Mr Leigh - said the trio were very disappointed but respected the decision.

''This is a sad day for those same-sex couples that took advantage of the ACT's … legislation and tied the knot since Saturday,'' they said.

''The Prime Minister must now deliver on his pledge that the Liberal Party room will revisit the question of whether to have a conscience vote on same-sex marriage.

''The Abbott government chose to mount this legal challenge at a cost to taxpayers when this is an inherently political decision that should be decided in the Federal Parliament.''

Democratic Labour Party senator John Madigan said the only way to settle the issue was by a referendum.