Tony Abbott says he'll respect the outcome of a postal vote on same-sex marriage whatever the result, but will be advocating the "no" case.
Ballot papers will hit mailboxes in mid-September after the Senate again rejected a compulsory plebiscite and the government triggered its backup plan of a $122 million postal ballot.
All responses will have to be received by November 7, with the result announced on November 15.
While there will be no publicly-funded "yes" and "no" cases, Malcolm Turnbull and Bill Shorten are in favour of the law change while Mr Abbott backs a "no" vote.
However, a High Court challenge could derail the ballot altogether.
Independent MP Andrew Wilkie and marriage equality advocates Shelley Argent and Felicity Marlowe have initiated the court action, having been advised there are constitutional problems with the Australian Bureau of Statistics running the poll and the government paying for it without parliament's approval.
Mr Abbott says he'll respect the verdict of the people.
"In politics you win some, you lose some," the former prime minister and leading Liberal conservative told Sydney's 2GB radio.
However he will put the case that the traditional definition of marriage should not change.
Labor shadow attorney-general Mark Dreyfus said while many people did not like the postal ballot, it was happening and "we have to win it".
Acting special minister of state Mathias Cormann has reassured people they will have plenty of time to enrol to vote and update their electorate details ahead the postal poll.
He declined to give an exact time frame but said the ABS statistician would make an announcement soon.
"There will be appropriate arrangements in place for new voters to enrol onto the electoral roll and existing voters whose circumstances have changed to update their details," he told ABC Radio.
"The arrangements will be broadly consistent with those that apply in the context of a federal election."
Asked about protections against gay-hate flyers being put in mailboxes, Senator Cormann said: "we trust the Australian people will be able to conduct this debate courteously and respectfully."