The latest poll shows 64 per cent of voters in the marriage equality survey said they voted Yes.
The Guardian poll suggests a strong victory for marriage equality, with results to be released next week.
Just 31 per cent of those polled said they voted No, with another 5 per cent declining to reveal their vote to the poll.
While Prime Minister Malcolm Turnbull has said he supports marriage equality, the matter still must go to a parliamentary vote in the event of a Yes victory for the postal survey.
Anti–marriage equality campaigner Tony Abbott has said the No campaign will continue fighting against changes to the Marriage Act.
Alex Greenwich, independent MP and co-chair of the Equality Campaign, has said there is no reason marriage equality shouldn’t be in effect by the end of this year.
“We have a very robust marriage equality bill. There’s no need for any more process. We’ve got the bill—it’s time for parliament to get this done,” Greenwich said last week.
Polls over several years have consistently shown majority support for marriage equality in Australia.
The official results of the postal survey will be revealed on November 15.