Prime minister Malcolm Turnbull says the mechanism for the same-sex marriage plebiscite will be "as close as possible" to a referendum, which could make it much less likely to return a "yes" result.
Turnbull said the details were yet to be finalised, but confirmed that it in design it will resemble a referendum.
"I expect the plebiscite to be very similar to the mechanism used for a referendum. Unlike the UK, for example, where the Brexit referendum was something of a novelty, in Australia we are used to having votes on big constitutional issues. It will be very close to that, that would mean if there is any funding made available for the 'yes' or 'no' case, the funding would be made on a strictly equal basis."
The referendum mechanism is “appropriate, it’s fair, it’s well-accepted, it’s standard procedure,” he said.
Australia is notoriously cautious about passing referendums, which require a majority of people in a majority of Australian states to pass.
Of the 44 referendums held in Australia, only eight have passed.
A 2014 poll conducted by Crosby Textor and commissioned by Australian Marriage Equality found majority support for same-sex marriage in NSW (75%), Victoria (72%), South Australia (71%), Western Australia (68%) and Tasmania (60%).
But a Coalition spokesperson contacted BuzzFeed News after Turnbull's press conference to clarify that "only a simple majority will be needed for the plebiscite, not the majority of states formula used in referendums".
Turnbull did not confirm whether compulsory voting would apply to the marriage plebiscite.
Referendums are also usually binding votes, whereas a plebiscite is an advisory poll.
Turnbull was also pressed on how he can guarantee the passage of same-sex marriage through the parliament if the Australian people vote "yes".
For same-sex marriage to be legalised via a plebiscite, a bill must also be passed through the parliament.
Turnbull insisted that he knows parliamentarians well enough to be able to guarantee the bill would pass the parliament.
“There are few things in politics that are certain. But one thing that is an absolute certainty is that same-sex marriage will pass the parliament if the plebiscite passes.”
“It will sail through the parliament.”
“I have a very good understanding of parliaments, parliamentarians, and the realities of politics,” he said.
Turnbull also said he is "reasonably optimistic" that the plebiscite could occur towards the end of this year.
On Tuesday evening, senior ministers Scott Morrison and Julie Bishop repeatedly refused to clarify whether they would definitely vote "yes" in the parliament if the Australian people did so in a plebiscite.