The federal Labor caucus will allow its deputy leader to introduce a private bill to parliament that aims to legalise same-sex marriage.
But the bill's introduction will be subject to Liberal MPs being allowed a conscience vote.
"Marriage equality's time has well and truly come," Tanya Plibersek said in a statement after a meeting of the caucus in Canberra on Tuesday.
She called on the prime minister to allow his MPs and senators a free vote on the bill.
"Liberal MPs pride themselves on being able to cross the floor on issues - Tony Abbott needs to confirm that includes marriage equality."
The text of the bill is similar to legislation introduced by Labor MP Stephen Jones which parliament voted down in 2012.
Ideally, Ms Plibersek would like a Liberal MP to co-sponsor the bill.
The Australian Greens warned Labor risked jumping the gun by pushing legislation before an informal cross-party committee could make recommendations to get consensus across parliament.
"I hope this isn't just a stunt before Mardi Gras," deputy leader Adam Bandt said in a statement.
Labor rushed the Jones bill to a vote before work was done to get Liberal backbenchers on board, he said.
"We don't want that to happen again."
