The US Supreme Court  decision to invalidate bans on same-sex marriage is expected to galvanise movement towards a marriage equality decision in Australia, as pressure builds for a vote to be held this year.

In a 5-4 ruling, the US Supreme Court determined that state bans on same-sex marriage were unconstitutional, thereby legalising gay marriage in all 50 states.

National director of Australian Marriage Equality, Rodney Croome, said he had discussions with several Liberal Party MPs over the past few weeks who had indicated the US decision would influence their position.

"Many Australian politicians on both the left and the right look to the US for leadership on issues of the day and will find the Supreme Court decision quite compelling," he said.

"I've spoken to a number of centrist Liberals who have indicated to me that this decision will be pivotal to them because it will establish, once and for all, whether same-sex marriage is a civil right, and that is important to them."

Prime Minister Tony Abbott has previously indicated the Liberal party room would decide whether its members should be given a conscience vote on the issue. He has criticised a private member's bill from Opposition Leader Bill Shorten, arguing that any resolution on same-sex marriage should be "owned by the parliament" rather than one party.

At the Liberal federal council meeting on Saturday, Mr Abbott said he "noted" the US decision but reaffirmed his personal opposition on the issue.

"What happens in the United States is a matter for the United States, just as what happened in Ireland a few weeks ago is a matter for the Irish," he said.

"I have views on this subject which are pretty well known and they haven't changed."

Education Minister Christopher Pyne, who has previously voted against same-sex marriage, described the US ruling as "fascinating" and acknowledged there was growing momentum for marriage equality worldwide.

He said gay marriage was not something the High Court of Australia could make a similar decision on, but would become an issue for parliament after the winter recess.

"When we come back in spring there's every possibility that that will be back on the agenda and there will be a vote on it and the parliament will either own it or defeat it," Mr Pyne said.

He said the issue should be dealt with this year, before the next election.

Queensland backbencher Warren Entsch, a prominent Liberal campaigner for marriage equality, said the Supreme Court ruling would buoy supporters of reform within the party.

"I'm sure people will talk about it, there's no doubt about it," he said. "I don't know whether it will change too many views, though."

There would always be a group who say "no way in the world" to marriage equality, and Mr Abbott was unlikely to ever change his mind, Mr Entsch said.

Tom Switzer, a research associate at the United States Studies Centre with close links to the Liberal Party, said the Supreme Court decision was a "cultural watershed moment" for America.

He said the ruling would affirm the "wake-up call" many parliamentarians received when staunchly Catholic Ireland voted in favour of gay marriage at a referendum in May. He echoed previous comments by Mr Abbott's lesbian sister, Christine Forster, who said the reform was "inevitable" and that the Liberal Party's position was shifting.

"She's probably right when she says there'll be dramatic changes and they'll come within the next year," Mr Switzer said.

Speaking to reporters in Melbourne, Mr Shorten said the US was "very influential" in Australian culture and governance, and called on Mr Abbott to grant a conscience vote on the existing private member's bill or to put forth a government-sponsored bill.

Labor's Penny Wong, who has called for the ALP to adopt a binding position on marriage equality at its national conference, heralded the US decision as "a wonderful step forward".

"It emphasises that not only is Tony Abbott out of touch with the Australian community, he's increasingly out of step with democracies everywhere," she said.

The Australian Christian Lobby also issued a statement, in which it condemned the ruling as the final step in an "undemocratic march to redefining marriage" that had been conducted by "unelected judges".

"It is hard for Australians to understand why the US system allows the courts decide contentious social policy," managing director Lyle Shelton said.

"It is so important that here in Australia these matters remain with the people through democratic processes."

The latest Fairfax/Ipsos polling showed 68 per cent of Australians supported legalising gay marriage.