Big Dave Foster is a good man to have on your side in a scrap.

Today, when the Greens introduce a motion supporting gay marriage to the Tasmanian Parliament, the world champion axeman will be on their side.

One of his four children, daughter Sally, is gay and has a 1-year-old child with her partner, and Foster wants to walk her down the aisle.

"If you'd asked me [about same-sex marriage] 15 years ago I would have had a completely different answer for you," he told a forum on the issue.

Advertisement

"But it's amazing, as you get older in life you have to change views and I think that's a good thing and I think our world has changed so much.

"I've been lucky enough to walk down the aisle with my eldest daughter, my son got married and as a parent that is one of the most treasured things."

The motion to be tabled today by state Greens leader Nick McKim and debated tomorrow will be a scene-setter for Labor's national conference in December, at which gay marriage will be on high on the agenda.

The move is opposed by Prime Minister Julia Gillard, who lives in a de facto relationship with partner Tim Mathieson, but had strong support within the party.

Among those advocating changes to the marriage act is Finance Minister Penny Wong, who last month announced she and partner Sophie Allouache were expecting a child.

Federal law does not allow same-sex marriages, nor does it recognise gay marriages performed overseas.

But the Australian Capital Territory performs civil partnerships, they can be recorded on domestic partnership registries in Tasmania, Victoria and New South Wales, and all states accept gay couples as de facto relationships.

Gay partners are also entitled to tax-free superannuation payments and same-sex couples are entitled to tax, health, social security and other benefits applying to unmarried straight couples.

Advertisement

Polls in the past few years have shown consistent support for legal same-sex marriage - the most recent was a Galaxy poll last month reporting 78 per cent of respondents favouring a conscience vote on the issue.

The poll also said 60 per cent favoured marriage equality, including 74 per cent of Labor voters and 48 per cent of Coalition supporters.

More than 50 per cent of Australians who identified as Christians were in favour of the change.

In Tasmania, Labor is hedging its bets on the issue, while the Liberals reject same-sex marriage.

The Greens' motion calls for in-principle support for gay marriage and calls on the Federal Parliament to change the marriage act.

McKim said if the Federal Parliament did not act this year the Greens would introduce a state bill to legalise same-sex marriage in Tasmania.