The move to legalise gay marriage in Australia is gaining momentum and likely to happen before the end of the year, with another government MP signalling he is willing to cross the floor to support change, and a Liberal senator warning failure to recognise marriage equality would be "political suicide."

On Monday, the federal Liberal MP for Brisbane, Trevor Evans, said he supported a free vote. His comments are being interpreted by supporters of gay marriage as a coded signal that he would be willing to cross the floor to help bring on a vote and force the issue to be dealt with by Parliament.

Mr Evans - who is openly gay - told News Corp the Coalition should dump its policy to hold a plebiscite on the issue given it has been rejected by Labor and the Greens in the Senate.