Julia Gillard has used her de facto relationship with partner Tim Mathieson to justify her opposition to gay marriage.
Appearing on ABC TV's Q&A program last night, the Prime Minister said it was her own experience that it was possible to be in a loving and committed relationship without marriage.
"I of all people - and I think people in this room and beyond this room know a bit about my personal life - I of all people would sit before you and say I think you can have a relationship of love, and commitment and trust and understanding that doesn't need a marriage certificate associated with it," Ms Gillard said.
"That is my life experience and I'm speaking from that life experience.
"It then becomes a question if you believe as I do that people can have deep and committed relationships without a marriage certificate."
Ms Gillard gave the answer when confronted by Vietnam veteran Geoff Thomas, who demanded to know why his gay son should not be allowed to marry his long-term partner.
Mr Thomas asked a similar question in 2010 of Opposition Leader Tony Abbott when he appeared on the program.
Parliament is set to debate legislation later this year that would allow gay marriage.
Ms Gillard has given her MPs a free vote on the issue but Mr Abbott has vowed to fight the legislation.
"I've taken a particular view about it. It's a view that some might look at me and think that it is an odd one for her to hold but it is one that I hold very deeply," Ms Gillard said.
She would not be drawn on the attacks senior ministers launched against Kevin Rudd to in the run-up to the leadership ballot that helped her to a resounding victory. "Colleagues told the truth from their perspective about how they believed it was the best way forward for Labor and Labor colleagues made up their mind," she said.
"The leadership contest is done, it's finished, people made their contributions during it. It's not my intention to re-canvass those contributions."
With the Government and her own approval languishing in the polls, Ms Gillard she had been "driven to do some really big things" such as introduce the carbon tax but acknowledged that "politically it's been difficult days" for Labor.