It looks like Australia will be heading to a postal plebiscite, after today's second attempt to revive a plebiscite was defeated.
The senate failed to reach a majority vote on the bill this morning, with the Senate voting 31-31 not to hold a second reading debate on the bill.
Ballot papers are expected to be posted from September 12 with voters given until November 7 to return their ballots and a result declared on November 15.
If there is a majority "yes" vote in the $122 million poll, the parliament would debate and vote on a private member's bill to change marriage laws in the final sittings for the year.
However, if the result is "no" the government won't take any action, leaving it to renegade Liberal MPs and Labor to bring on a bill for debate if they want to pursue it.
Marriage equality campaigners are seeking legal advice on a possible court challenge to the postal ballot, which will be run by the Australian Bureau of Statistics.
Labor frontbencher Penny Wong said the parliament should debate and pass changes to marriage laws now, rather than waiting for the results of an "expensive stunt".
Senator Wong, who is in a same-sex relationship, said many in the Liberal-Nationals coalition could not countenance equality and were never going to change their minds whatever the result of the poll.
"They simply cannot countenance people like me and others being equal - simple as that," she told parliament on Wednesday.
She objected to the Australian Christian Lobby describing the children of same-sex couples as the "stolen generation" and rejected Senator Cormann's statement the plebiscite could be a "unifying" decision for the country.
"You talk about unifying moments? It is not a unifying moment. It is exposing our children to that kind of hatred."
Senator Cormann said the Australian people should have their say and the vote would honour the coalition's 2016 election promise.
"We have a constitutional way to keep the faith with the Australian people from the last election, to give them part of the say in the decision-making process on whether or not our laws should be changed ... to allow same-sex couples to marry," he said.
Former prime minister Tony Abbott, who opposes same-sex marriage, earlier told reporters Mr Turnbull should be congratulated for allowing the vote to go ahead.
He framed the debate much wider than a question about changing marriage laws.
"If you don't like same-sex marriage vote 'no', if you're worried about religious freedom and freedom of speech vote 'no', if you don't like political correctness vote 'no'," Mr Abbott said.