Liberal MP Wyatt Roy has confirmed he will defy Prime Minister Tony Abbott and cross the floor to support same-sex marriage, should a vote be allowed.

In an interview with Buzzfeed on Thursday, Mr Roy – Australia’s youngest ever Federal MP – said he had long been a supporter of same-sex marriage and would vote accordingly.

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“I think the parliament can deal with it,” Mr Roy said.

“I’m from a very socially conservative Queensland electorate but I told my constituents when I was first elected, I’m for same sex marriage and nothing will change that.”

However, the Queensland MP is unlikely to get the opportunity.

Prime Minister Abbott quashed a push from within his party to allow a free vote on the issue and has warned ministers to follow the party line.

Government frontbenchers have been talking up the chances of putting the issue to a popular vote through a plebiscite or referendum, but only after the next election.

Asked if he would cross the floor to vote against the Coalition, Mr Roy said: “I feel quite comfortable doing that”.

The cross party bill put forward by Liberal MP Warren Entsch will be introduced into the lower house next week, but a debate or vote is now unlikely to occur.