Just one electorate in the country has a majority of voters opposed to same-sex marriage, according to new research that suggests MPs and public debate significantly trail voters in backing change.
The University of Melbourne-led study found opposition to changing the Marriage Act ranges from 40 to just over 50 per cent in a handful of rural Queensland and northern NSW seats to less than 10 per cent in inner-city electorates in Sydney and Melbourne.
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Maranoa, in outback south-western Queensland and held by the Coalition's David Littleproud, has just over 50 per cent of voters who do not want a change to allow same-sex couples to wed.
A small collection of seats – Groom, Flynn and Hinkler in Queensland and Deputy Prime Minister Barnaby Joyce's base in New England – could oppose same-sex marriage if undecided voters opted for the status quo.
But in most seats a clear majority backs marriage equality.
Support is strongest in the Sydney seats held by Labor's Tanya Plibersek and Anthony Albanese, Prime Minister Malcolm Turnbull's home turf of Wentworth, Greens-held Melbourne and a ring of ALP seats in the Victorian capital's inner suburbs.
The study – based on responses to the ABC's Vote Compass survey in 2013, weighted in analysis to reflect the demographics in each electorate – found only a third of voters were opposed to a change.
The push for marriage equality appears likely to stall in this parliamentary term, with Labor and the crossbench opposed to a plebiscite and the government pledged to block a change unless there is a national vote.
![Families opposed to a plebiscite on same-sex marriage rally outside Parliament earlier this month.](/web/20160926190951im_/http://www.smh.com.au/content/dam/images/g/r/e/w/1/m/image.related.articleLeadwide.620x349.grn2mq.png/1474844354504.jpg)
One of the researchers, Monash University political scientist Shaun Ratcliff, said that while the study was not a direct poll of voters it showed the vast majority of electorates wanted change.
"Based on our data and other polling, it appears a plebiscite would pass easily," he said.
The study found a significant divide in opinion between rural and urban areas. Every rural and regional electorate in the country has below-average backing for change, while support is above average in inner-city seats of every capital city.
It also found the stronger the support for legalising same-sex marriage in an electorate, the more likely an MP was to publicly support the change. There was a significant shift between 2012 and 2015, with MPs from both major parties changing their position, but politicians were still lagging behind the public.
Whereas a clear majority of voters support change, the study estimates that MPs in the House of Representatives would only narrowly back it if given a free vote, based on their public statements.
Mr Ratcliff said this may, in part, be due to the influence of interest groups.
"Politicians represent a number of different interests including their constituents, and also generally have a status quo bias, which is not necessarily a bad thing as they are expected to be cautious," he said.
"But at the same time there has been a majority in favour of same-sex marriage for quite a long time now. I don't think anything's inevitable but suspect on this particular issue we're going to see same-sex marriage legalised. It's just a matter of when."
The researchers, including the University of Melbourne's Andrea Carson and Yannick Dufresne from Canada's Universite Laval, will present the study at an Australian Political Studies Association conference at the University of NSW this week.
Ten electorates most opposed to same-sex marriage
Maranoa*, QLD (LNP, David Littleproud)
Groom, QLD (LNP, John McVeigh)
Flynn, QLD (LNP, Ken O'Dowd)
Hinkler, QLD (LNP, Keith Pitt)
New England, NSW (Nationals, Barnaby Joyce)
Kennedy, QLD (Katter's Australian Party, Bob Katter)
Grey, SA  (Liberal, Rowan Ramsey)
Barker, SA (Liberal, Tony Pasin)
Parkes, NSW (Nationals, Mark Coulton)
Braddon, TAS (Labor, Justine Keay)
*The only seat where a majority was opposed.
Ten electorates most supportive of same-sex marriage
Sydney, NSW (Labor, Tanya Plibersek)
Melbourne, VIC (Greens, Adam Bandt)
Grayndler, NSW (Labor, Anthony Albanese)
Wentworth, NSW (Liberal, Malcolm Turnbull)
Melbourne Ports, VIC (Labor, Michael Danby)
Wills, VIC (Labor, Peter Khalil)
Gellibrand, VICÂ (Labor, Tim Watts)
Batman, VIC (Labor, David Feeney)
Higgins, VIC (Liberal, Kelly O'Dwyer)
Brisbane, QLD (Liberal, Trevor Evans)