Sydney same-sex marriage rally: Tony Abbott's sister Christine Forster among speakers at demonstration

A bill on the issue is being introduced on Monday in Australia

Crowds gather at Taylor Square during the demonstration (Getty Images)

More than a thousand people took to the streets of Sydney on Sunday to rally in favour of equal marriage in Australia.

Christine Forster, Liberal Party politician and the gay sister of the Australian Prime Minister Tony Abbott, was among the speakers at the demonstration.

It came days after Mr Abbott seemingly bowed to pressure by hinting that he would allow his MPs a free vote on a same-sex marriage bill which will be introduced in federal parliament on Monday.

Although Ms Forster is engaged to a woman, the Prime Minister has been a long standing opponent of gay marriage, and rejected calls for a referendum after Ireland's public vote earlier this month reignited debate on the issue in Australia.

However, on Wednesday Mr Abbott changed his stance, allowing his Liberal Party politicians a conscience vote on the bill put forward by Bill Shorten, the leader of the opposition Labor Party, which could pave the way for a change of the law as early as August.

The bill will change the wording within the country's Marriage Act to replace "man and woman" with "two people", while recognising the union of same-sex couples who have married overseas.

Addressing the rally, Ms Forster introduced her "beautiful fiance" Virginia Edwards and said: "Why wouldn't I marry this beautiful woman as soon as I possibly could?"

Ms Forster has backed calls from Mr Shorten for a bipartisan, cross-party bill on the issue, to avoid gay marriage being turned into a "political football".

Christine Forster (L) and Virginia Edwards address the rally (Getty) (Getty Images)

The deputy leader of the Labor Party, Tanya Plibersek, also spoke at the demonstration. “This is the last piece of unfinished business to full equality for gay men and lesbians in this country," she said.

“Like one of our greatest Labor prime ministers said, men and women of Australia, it’s time.”

After Ireland voted overwhelmingly in favour of equal marriage Australia is now the largest developed, English-speaking country that bans same-sex couples from marrying within its borders.

The issue was last debated in the nation's two parliaments in 2012, when a bill to amend existing laws was comprehensively defeated.