Prime Minister Tony Abbott said this would be the last term in which the Coalition would be bound to vote against same-sex marriage, following a marathon six-hour debate in the Coalition party room on the issue.

The outcome was announced after a lengthy, robust discussion which decided not to give Federal MPs a free vote on the matter, ahead of a cross-party bill to be introduced into parliament on Monday.

After the meeting Mr Abbott said there was strong support among his MPs for maintaining the traditional definition of marriage between a man and a woman.

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Reports indicated the free vote for party members was defeated 66-33 – with just three out of 21 Nationals voting for it.

“The Coalition will hold its current position on binding a vote for the remainder of this term (of parliament),” Mr Abbott told reporters after the meeting.

“I come to a view … that this is the party room view … that this is the last term that the party room can be bound to vote against same-sex marriage.

“Going into the next election, we will finalise another position.

“The disposition of the party room this evening is that our position going into the next election should be that in a subsequent term of parliament, this is a matter that should rightly be put to the Australian people.

“We have not finalised a position to take to the next election, we have finalised a position for the duration of this term.

“Going into the next election we will have more to say, but the disposition is that in the next term of Parliament, we will put it to the people.”

He flagged either a plebiscite, or constitutional referendum if elected to another term of government.

“In the next term of parliament we will put it to the people for the people to decide in the next term of parliament,” Mr Abbott said.

“The focus of debate on the particular subject won’t be MP’s it will be on the Australian public as a whole.”

Mr Abbott said, however, there was much support from within the party room for the existing policy.

“There was strong support for the existing policy that marriage is between a man and a woman,” he said.

“It you support marriage as being between a man and a woman the Coalition is on your side.”

Liberal MP Warren Entsch’s same-sex marriage bill will be introduced to parliament on Monday, but a debate and vote may never eventuate.

The bill has the support of Labor, The Greens and some independent MPs.

Mr Entsch conceded his cross-party bill was doomed to fail.

“Given today’s decision, the likelihood of failure – should it come to a vote – is assured,” he said in a statement.

He will instead take the opportunity for debate to highlight personal stories that led him to support same-sex marriage.

Earlier on Tuesday, Education Minister Christopher Pyne warned the PM against the move, saying he could be accused of “branch stacking”, given so few Nationals MPs support gay marriage.

Opposition Leader Bill Shorten released a statement on Twitter after Tuesday night’s decision was announced.

Australia stuck in the past under @TonyAbbottMHR – It’s time for #MarriageEquality

— Bill Shorten (@billshortenmp) August 11, 2015

After the meeting, young Queensland Liberal National MP Wyatt Roy told reporters it was great for everyone to have their chance to discuss their views, but did not reveal which way he voted.

Greens MP Adam Bandt said Mr Abbott has signed the death warrant on his government after siding with a “vocal homophobic minority”.

“Because within a year they will be out of office,” he told parliament on Tuesday night.

Greens Senator Janet Rice urged Liberal MPs to cross the floor and back the Greens bill for same-sex marriage, which is scheduled for debate in the senate in November.

Abbott’s sister talks of hope

Mr Abbott’s sister Christine Forster could only talk about hope as the meeting proceeded on Tuesday night.

Ms Forster, a Liberal City of Sydney Councillor who is gay and a vocal advocate for marriage reform, has challenged the Prime Minister in recent months to allow his MPs a free vote.

“I’m feeling very disappointed and … I fervently wish the vote had gone the other way,” she told the ABC’s Lateline.

“For me it goes to core Liberal principles [by] which we are all equal before the law.

“It’s my view … that our Liberal MPs, our Coalition MPs … should have been given the opportunity to vote with their consciences on this.

“They could all stand on their principles and look their constituents in the eye and say ‘I voted this way because that is how I believe, that is my personal belief’,” she said.

-with agencies