The new campaign group is led by Andrew Bragg, who was until recently the acting federal director of the Liberal Party, and hopes to persuade voters of the case for same-sex marriage within the liberal and conservative traditions embodied by the Liberal Party.

If marriage equality becomes a legal reality, this will allow everyone to make choices based on their personal convictions. Credit:AAP

The campaign has released a short ad in which a series of voters declare it is time to vote "yes" for same-sex marriage, while also declaring their allegiance as Coalition voters.

Mr Greiner said he had joined the "yes" campaign because one of his children, Justin, could get married and the other, Kara, could not – and that struck him as fundamentally unfair.

"I have two kids, one of whom is in a model of a traditional marriage, one of of whom is in a model of a same-sex relationship. I don't see how in heaven's name we can ask their kids [Mr Greiner's grandchildren] to think it's acceptable that one partnership is inferior to the other," he said.