Labor leader Bill Shorten will move to legalise same-sex marriage in his first 100 days if he becomes prime minister.
Mr Shorten made the pledge after securing a compromise that federal Labor MPs would be bound to vote in favour of marriage equality, but not for another two elections.
Labor has tried to put a potentially damaging internal rift over the issue behind it by challenging Prime Minister Tony Abbott to allow his members a free vote on the issue.
Mr Shorten said same-sex couples had waited too long for marriage equality.
"Australia is trailing the world," he said.
"The debate about marriage equality has simply gone on too long."
Mr Shorten said same-sex marriage legislation could pass the present parliament, calling on Mr Abbott to allow Liberal MPs a free vote.
"I know that there is a great deal of debate about 'is the best and fastest way to make marriage equality a reality to allow every member of our parliament to have a free vote'," he said.
"What the Labor Party does with this resolution is we lay down the challenge to Mr Abbott and his Liberals: Please give your members of parliament a free vote so we can make marriage equality a reality now."
The ALP's Left faction has been split over the issue of a binding vote or the current conscience vote.
The compromise resolution means federal Labor MPs will be bound to vote for same-sex marriage if a bill is put before the parliament, but not until after the next two elections.
Mr Shorten's 100-day pledge means that if the ALP wins the 2016 federal election, its MPs will still have a conscience vote rather than a binding one.
Deputy leader Tanya Plibersek, whose Left faction wanted the binding vote, said she was "delighted" to second the compromise resolution.
"The current parliament has the numbers to pass marriage equality and should be allowed to," she told delegates.
"I still hope we can have marriage equality by Christmas, but if this parliament doesn't pass marriage equality, a Shorten Labor government will in its first 100 days."
Senior Labor frontbencher Penny Wong, who has a same-sex partner, said the decision would end a conscience vote on a matter "that should never have been a conscience vote".
"I hope more of you will join us, but most of all I hope those in the Liberal Party who are truly liberal will join us to end discrimination because there is nothing to fear from equality," she told Labor delegates.
Liberal frontbencher Peter Dutton said nothing the Labor conference decided would affect how the coalition responded to the same-sex marriage issue.
"We took a position to the last election - we should adhere to that position and we should adopt it going to the next election," Mr Dutton told Sky News.
