Tony Abbott's daughter supports the YES case

TONY Abbott's daughter Frances Abbott has declared she will vote in favour of legalising marriage equality in Australia's postal survey.

Despite her father being a leading figure in the No campaign, Ms Abbott has thrown her support behind the Yes case, posting a smiling photo of herself in a "vote yes" T-shirt.

"I don't really care much for politics," she posted on Instagram.

"But I do really care a lot for love. All love is good. Let's celebrate it."

Ms Abbott followed up with a string of pro-same sex marriage hashtags, including #getaroundit, #comeonaustralia, #itstime and #lovewillwin.

The gay marriage debate has divided the former prime minister's family, with Mr Abbott engaging in a public war of words with his sister Christine Forster, a Sydney councillor and marriage equality advocate.

Mr Abbott recently said his sister "joked years ago that she'd just got herself out of one marriage - why would she be rushing into another one?".

His sister, who is now in a same-sex relationship, hit back and said Mr Abbott's comments were "hurtful".

But she said they had agree to disagree in the debate.

"The Abbott family is like every other family. We do have differences of opinion on some things but we are a normal, functional family," Ms Forster said.

"We're brother and sister. We love each other. In all other respects we try to get along."

In a recent column for The Australian, Mr Abbott said: "Same-sex marriage is a tough issue. It divides families; it splits political parties; often enough, it tears at individuals, too."