After years of delay, the issue will now dominate Parliament in the final weeks of 2017, with a fierce political stoush over protections for religious freedom looming, an extra sitting week a live option and a swag of amendments to Liberal senator Dean Smith's bill in the offing - though major changes to the bill are considered unlikely.

In a thumping victory for supporters of change, 61.6 per cent of Australians voted "yes" and 38.4 per cent voted "no". Every state and territory in the country voted "yes", while 133 of 150 federal electorates voted "yes" and just 17 said "no".

At street parties across the country, gay and lesbian Australians cheered, danced and embraced as the results were announced by the chief statistician on Wednesday and Australia - which was one of the first countries to give women the vote - finally voted to join 25 other countries around the world that have allowed same-sex marriage.

Prime Minister Malcolm Turnbull hailed the "unequivocal" and "overwhelming" victory. "They voted 'yes' for fairness. They voted 'yes' for commitment. They voted 'yes' for love," he said. "Now it is up to us, here in the Parliament of Australia, to get on with it".

Mr Turnbull stopped short of guaranteeing same-sex marriage would be legalised before Christmas, but senior figures in the Turnbull government said it was "unthinkable" Parliament could rise without the law being passed.

With just two more weeks of Parliament scheduled, conservative forces have begun work on amendments to the Smith bill that would - they argue - provider greater protections for religious groups and for freedom of speech.

Treasurer Scott Morrison signalled plans to move amendments to the proposed laws and Immigration Minister Peter Dutton will also get involved, while junior ministers and conservatives Michael Sukkar and Liberal Zed Seselja will also play a key role.

As Senator Smith swiftly introduced his bill on Wednesday, Attorney-General George Brandis flagged his intention to bring amendments allowing civil celebrants - not just ministers of religion - the right to decline to perform gay weddings, as well as a clause clarifying it is not unlawful for anyone to hold or express a view on same-sex marriage.

Labor's Penny Wong, a long-time marriage equality advocate who was in tears when the results were announced, warned: "The Australian people voted to remove discrimination and I trust the bill will reflect that."

Victoria recorded the second-highest level of support (64.9 per cent) behind the ACT's 74 per cent. Victorians also had the second-highest participation rate in the voluntary survey, after the ACT, at 81.7 per cent - or 3,317,755 people.

Greens MP Adam Bandt's inner-city seat of Melbourne returned the equal-highest "yes" vote in the country at 83.7 per cent, the same as Tanya Plibersek's seat of Sydney.

Not a single Liberal or National seat in Victoria voted against same-sex marriage. The two seats to say "no" were the Labor-held suburban electorates of Bruce and Calwell. Labor MPs Julian Hill and Maria Vamvakinou confirmed they would vote "yes" in the Parliament anyway.

The "no vote proved far more successful in Sydney, where several Labor frontbenchers with seats in the city's west found themselves out-of-step with their "no" voting constituents.

Former prime minister Tony Abbott, a vocal opponent of same-sex marriage, saw a massive 75 per cent of people vote "yes" in his seat of Warringah. He congratulated the "yes" campaign and said he wanted improvements to the Smith bill "to implement same-sex marriage with freedom of conscience for all, not just the churches".

A handful of politicians have vowed to ignore the result and vote "no" or abstain, but many Liberal opponents of same-sex marriage - such as Mr Sukkar, Craig Kelly and Ian Goodenough - have said they will now vote "yes" in line with the wishes of voters in their seats.

Regional Australia largely swung behind the "yes" campaign, with 15 of 16 Nationals-held electorates supporting same-sex marriage, despite only a handful of Nationals MPs backing the change.

All told, 12,727,920 Australians or 79.5 per cent of the country voted in the postal survey, which was fiercely criticised by same-sex marriage advocates and Labor as a cruel and unnecessary vote on civil rights.

The coming debate on the law change is already being compared to the 2006 debate over abortion drug RU486, on which MPs were also granted a conscience vote.

Three groups of MPs within the Coalition are expected to emerge in the coming weeks: a "yes" group, a "no" group of MPs who had opposed same-sex marriage but will propose "sensible" amendments, and a "hard right" grouping.

The final version of the bill, however, is unlikely to be vastly different given any amendments would need to be supported by a majority in both chambers.

Victorian Liberal senator James Paterson has already dumped his controversial alternative bill, conceding it did not have his colleagues' support, but some of the amendments to the Smith bill will be drawn from his proposal.

In particular, Mr Morrison outlined a series of changes including the ability for parents to withdraw their children from schools if they were taught about same-sex marriage, protections for religious organisations that currently have tax-deductible status or receive public funds, and a "no-detriment" clause for people who believe in traditional marriage.

Debate will begin on Thursday on the laws, but will get under way properly in the Senate from November 27, before moving to the House of Representatives.

In front of supporters gathered in Sydney, the leaders of both campaigns were conciliatory, with "no" leader Lyle Shelton admitting defeat but arguing "no question is ever completely closed" and holding out hope of eventually persuading voters to reverse the change.

Tiernan Brady, director of the Equality Campaign, said he "never thought that winning was about beating people". "Victory cannot be making someone else feel excluded," he said.

But he warned politicians Australians had voted for equality "with the loudest possible voice", and the final bill could not be allowed to unwind anti-discrimination laws.

"That's not what Australia voted for," he said.