Throsby MP Stephen Jones's bill to legalise same-sex marriage was overwhelmingly defeated in the House of Representatives yesterday.
Mr Jones was disappointed by the 98-42 vote, but said change to the Marriage Act was inevitable.
"I think we've won the debate in the community, but we haven't yet won the debate in the Parliament," he said. "But I think it will happen at some stage in the next 10 years, hopefully sooner rather than later."
Mr Jones said it had been "pretty obvious" the bill would be voted down because Coalition MPs did not have a conscience vote.
"For as long as Tony Abbott refused to give his MPs a conscience vote, it was almost impossible for this bill to get up in this Parliament," he said.
"But this is an important issue that should be debated in the Australian Parliament because over 62 per cent of Australians believe that change is justified."
The vote came as Liberal senator Cory Bernardi resigned from the Coalition frontbench, under pressure from Opposition Leader Tony Abbott, after he suggested allowing gay marriage could lead to polygamy and bestiality.
Mr Jones welcomed Senator Bernardi's resignation, saying his comments "peddled fear, hate and prejudice".
Prime Minister Julia Gillard and Mr Abbott sat on the same side of the chamber to vote against Mr Jones's bill.
The government's frontbench was split on the vote, with Deputy Prime Minister Wayne Swan and cabinet minister Chris Bowen voting with the Coalition to oppose the bill. Former prime minister Kevin Rudd also voted to defeat the legislation.
Meanwhile, a same-sex marriage bill is expected to pass in NSW Parliament after party leaders announced they would let members have a conscience vote.
In a joint statement, members of a cross-party working group yesterday said they would soon draft a same-sex marriage bill for the state and were "optimistic" it would pass. However, NSW Opposition Leader John Robertson said it was too early to call the outcome of the vote.
"What I do know is a conscience vote will allow people to vote based on what they believe."