EMMA ALBERICI, PRESENTER: Tasmania is a step closer to becoming the first state in Australia to legalise gay marriage.

The Premier, Lara Giddings, today tabled a marriage equality bill in State Parliament.

It should pass the Lower House by the end of the week, but faces a tougher battle in the Legislative Council, the state's upper house.

Annah Yard reports from Hobart.

ANNAH YARD, REPORTER: A significant moment on what's being hailed a historic day.

LARA GIDDINGS, TASMANIAN PREMIER: It's with great pleasure that I, with my co-sponsor, the leader of the Greens Nick McKim, table the Same Sex Marriage Bill 2012.

ANNAH YARD: Only four weeks after announcing she would act on marriage equality, Lara Giddings has stayed true to her word.

RODNEY CROOME, GAY AND LESBIAN RIGHTS GROUP: That legislation gives us hope that we will some day soon be equal, and it sends a very important message to Canberra that they can no longer ignore this reform.

NICK MCKIM, TAS. GREENS LEADER: This is about doing the right thing and removing the discrimination that is enshrined in Tasmanian and Australian law, and I'm really proud to be a part of that.

ANNAH YARD: The legislation, which is based on bills Nick McKim's been trying to get through Parliament since 2005, will be debated on Thursday. But it's already sparked heated discussion.

WILL HODGMAN, TAS. OPPOSITION LEADER: There's more than a whiff of self indulgence in all of this, very much so, and there's very much also the undercurrent of the frailty of this Labor/Green government.

MARK BROWN, AUSTRALIAN CHRISTIAN LOBBY: I think it's a sad day when something like marriage, which has been around for thousands of years and served the community well, is seen as something that can, you know, be kicked around.

ANNAH YARD: Both the Christian lobby and the Opposition say a High Court challenge is inevitable.

WILL HODGMAN: Which will no doubt come at a cost to the Tasmanian Government.

ANNAH YARD: The Premier is confident the Bill will survive any challenge, and is more worried about the State's conservative Legislative Council. It's not likely to debate the issue until late next month.