Prime Minister Malcolm Turnbull will mark the one-year anniversary of his rise to power by introducing a Bill to parliament today that will allow for a plebiscite on same-sex marriage.

It is believed Cabinet has agreed to provide $7.5 million in public funding for both the yes and no campaigns, with a vote to be held on February 11 next year.

The question to voters will be whether the law should be changed to allow same sex couples to marry.

Several MPs have threatened to abstain from voting on the Bill or cross the floor.

The legislation is expected to pass through the House of Representatives but is considered unlikely to pass the Senate.

The coalition needs the support of nine senators for it to pass the Senate, with The Greens and the Nick Xenophon Team already declaring they will oppose the plebiscite.