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.

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.