COALITION MP Wyatt Roy has become the latest federal MP to throw his support behind same-sex marriage.

"I support the right of same-sex couples to have their loving and committed relationships recognised in state-sanctioned marriage," said Mr Roy, who at 23 is the youngest MP in Federal Parliament.

Mr Roy said he would support a free vote in the party room on the issue.

His announcement comes in the same week as former prime minister and fellow Queensland backbencher Kevin Rudd's decision to back same-sex marriage.

The conservative MP represents the seat of Longman, a semi-rural area outside Brisbane which includes the Caboolture Shire. Mr Roy said he was aware of the local community's views on the issue.

"I remain vigilant in regard to the views of my local community – and I continue to work through the issues and concerns," he said.

Gay marriage advocates today welcomed Mr Roy's decision. Australians for Marriage Equality spokesman Rodney Croome said his decision reflected a generational change in the Liberal Party.

"Wyatt Roy is representative of the strong support for marriage equality among young Australians, as well as the next generation of Liberals," Mr Croome said.

Mr Roy joins fellow Liberals NSW MP Malcolm Turnbull, Victorian MP Kelly O'Dwyer and South Australian senator Simon Birmingham in backing same-sex marriage.

Opposition Leader Tony Abbott said earlier this week that his opposition to gay marriage "certainly hadn't changed" and that he had given a commitment to the Christian lobby before the last election that he would not allow his MPs a conscience vote on the issue.

Mr Croome said Kevin Rudd's decision to support gay marriage, particularly significant because of his firmly held religious beliefs, had proved to be a watershed moment.

"Kevin Rudd's support for marriage equality is proving a game changer, especially in Queensland, with Wyatt Roy, as well as Mr Rudd's challenger, Bill Glasson, both coming out in support in recent days."

Mr Rudd said today he had noted Mr Roy's position.

"Does he also support Mr Abbott's refusal to grant a conscience vote?" Mr Rudd said. "Mr Abbott has effectively denied half the Australian Parliament the ability to exercise their individual consciences on this question - and their ability to vote one way or the other."

The changing politics of the issue in Queensland places further pressure on Brisbane Liberal MP Teresa Gambaro to get behind the issue, Mr Croome said. Ms Gambaro has sent mixed signals about her position on the issue.

"If the matter does come up, I expect it would be debated like any other matter," Ms Gambaro said. "I will respectfully listen to all views, reflect on the issue, talk to my community and talk to my colleagues."

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Daniel.Piotrowski@news.com.au