The Throsby MP will introduce a private member's bill to legalise same-sex marriage, setting the scene for a showdown with the Opposition and members of his own party, including Prime Minister Julia Gillard.

"To be honest, this is not what I entered Parliament to do, I've made it clear I'm a late convert on this and haven't really thought about it much before," Mr Jones said yesterday.

"But it's true I've had some personal experience where I had a cousin call me and say, 'Stephen I went to your wedding but you can't come to mine, so I'm asking you to support this' and I've considered the arguments for and against and frankly I see this as an expression of the core Labor values of fairness and equity."

Labor changed its platform to support gay marriage at its national conference in December but its MPs have only been granted a conscience vote.

This means Mr Jones' bill will only pass with the support of Opposition and cross-bench members.

The bill will not be debated or voted on for several months.

Australian Marriage Equality national convener Alex Greenwich conceded neither Mr Jones' bill, nor another co-sponsored by independent MP Andrew Wilkie and Greens MP Adam Bandt, would pass at the moment.

"It will be the first time a federal Labor MP will introduce a marriage equality bill and that in itself has a special place in history," Mr Greenwich said.

"I think it's going to send a really powerful message to gay and lesbian people within the electorate, as well as their families and friends."

Mr Jones, who has been criticised for his focus on same-sex marriage, stressed it was not his only priority.

"I think I've spoken in Parliament once on the issue of marriage equality and probably several dozen times on core economic issues, so I think I can walk and chew gum and have proven my ability to do that," he said.