Members of Tasmania's Labor Party are in Hobart for the annual state conference this weekend and are debating more than 150 motions.
Ms Giddings says the time has come for discrimination against gay couples to be removed and she has legal advice that says Tasmania can go it alone.
"We will be supporting legislation that will allow for marriage for gay couples here in Tasmania," she said.
"We will be removing that discrimination. We will be leading the way for the rest of Australia to follow."
And Ms Giddings says legislation could be passed before the end of the year.
"This is an issue that of course that has been in many respects dominating the social policy debate across Australia for some time now," she told Channel Seven.
"I have a fundamental view that there has been a tipping point that has reached where more in the community want this discrimination to be removed than those who don't."
Members of the party's right faction remained seated as the dominant Left members gave a standing ovation in support of the announcement.
Senator Helen Polley, from the Right, says there should not be any celebrations.
"I truly believe that the majority of Tasmanians are opposed to same sex marriage," she said.
'Keep the faith'
Prime Minister Julia Gillard used a pre-recorded message to address the conference, and urged members to keep the faith in her government.
"We will fight and fight hard because this is a contest of values, a contest for the soul of our nation, and a battle to protect all we have achieved and hold dear," she said.
"So keep the faith, keep believing, keep fighting and never, ever give in."
Acting Prime Minister Wayne Swan also addressed the party faithful, warning delegates that there was much at stake at next year's federal election.
He said Opposition Leader Tony Abbott planned to strip Tasmania of more than $600 million in GST revenue, as the Coalition had not ruled out backing the push from conservative states to distribute the tax on a per capita basis.
Pointing to the national broadband rollout and the national disability insurance scheme, Mr Swan said Tasmania was better off under Labor.
He also spoke again about his musical influences, after revealing earlier this week he had turned to US musician Bruce Springsteen for inspiration in his fight against Australia's mining magnates.
Mr Swan said it was a risky move and a conga line of "Tea Party wannabes" had criticised him.
"All those people, they'd be better off listening to a bit more music," he said.