Australian Attorney General George Brandis confirmed on Sunday the government would hold the vote before the end of the year if it is re-elected.
"The bill to constitute the plebiscite will be introduced early in the life of the parliament... in the event that there would be a yes vote the government would legislate to give effect to the wishes of the people," Senator Brandis told Sky News.
He added that there would be protection for religions who did not wish to conduct same sex marriage ceremonies in accordance with their faith.
Any change to the law would only impact the civil and secular definition of marriage, he stressed.
He said: "The protection of the rights of churches and religious people to conduct ceremonies of marriage in accordance with the teachings and liturgies of their faith is very important."
His promise of protection was cautiously welcomed by the Australian Christian Lobby.
Managing Director Lyle Shelton said: "While we welcome Senator Brandis' recognition that protection is needed for religious wedding celebrants, freedom of conscience rights must also be extended to people of faith or no faith who supply services to the wedding industry.
"In the United States and Europe bakers, florists, photographers and wedding chapel owners have all fallen foul of the law, and in some cases have incurred big fines, for exercising their conscientiously held views about the truth of marriage."
Mr Shelton said state-based anti-discrimination laws should be "set aside" in the run up to a referendum to give Christians the "freedom to discuss" the Bible.
He said: "This is not about licensing hate, it is about being able to discuss the basics of marriage... without the threat of legal action."
Australian Prime Minister Malcolm Turnbull is in favour of gay marriage but has called a referendum because of fierce resistance within his party.