TASMANIA has moved closer towards becoming the first Australian state to allow same-sex marriage with a bill passing parliament's lower house.

The island state is now an upper house vote away from becoming the country's first gay wedding destination, after the Same-Sex Marriage Bill 2012 sailed through the Legislative Assembly.

Labor Premier Lara Giddings announced the move earlier this month and, backed by partners in government the Greens, the bill passed despite Liberal opposition.

Labor and Greens members and onlookers, including Australian Marriage Equality chief Alex Greenwich, erupted into applause as the bill was passed.

During a long debate on the bill there were tears and quotes from the Bible as Labor and Greens members queued up to speak.

Liberal Leader Will Hodgman was the lone voice against the bill, saying his team was united in believing marriage was between a man and a woman, and a matter for the commonwealth.

For the first time in the state's history, a bill in the lower house was co-sponsored, by Ms Giddings and Greens Leader Nick McKim.

Ms Giddings declared it was the duty of 21st-century legislators to remove discrimination.

"I do not believe that the personal moral disapproval that some individuals may feel towards same-sex marriage is a valid reason to allow discrimination to continue in the 21st century," Ms Giddings said.

"In the 21st century moral disapproval is no reason to deny or curtail rights and freedoms.

"The denial of marriage to lesbian and gay couples and their families is discrimination that must be changed."

She pointed to the mental health benefits of marriage equality and said conservative leaders like New Zealand Prime Minister John Key, who this week backed same-sex marriage, and even some religious leaders had supported the move.

"Today we have an opportunity to lead the nation," she said.

"At the core of this debate is the belief that we are all equal before the law, and where the law prejudices one person over another change is required."

Mr McKim, who first tabled a same-sex marriage bill in 2005, said there was no such thing as "mostly equal".

"This is a pro-marriage, pro-family, pro-children bill," he told the chamber.

The bill will face an uncertain future in the state's upper house, where 13 of the 15 members are independents and several are yet to declare their position.

The Liberals say the move will expose Tasmania to a High Court challenge, but Ms Giddings says she has legal advice to the contrary.

Tasmania was the last state to decriminalise homosexuality, in 1997.

Marriage equality advocates have praised the parliament's vote.

Tasmanian Gay and Lesbian Rights Group spokesman Rodney Croome said if the laws passed it would forever banish the state's former reputation for homophobia.

The lower house had sent a message to federal parliament that states and territories would take the issue into their own hands if the commonwealth didn't act, Australian Marriage Equality national convener Alex Greenwich said.

Australian Greens senator Sarah Hanson-Young agreed, saying Tasmania's move put the federal Labor and coalition leaders to shame.

"If this reform continues to be blocked by the old parties at a federal level, the states and territories will take the lead and do what they know is right," Senator Hanson-Young said in a statement.

Originally published as Gay marriage a step closer in Tasmania