Qantas chief executive Alan Joyce says he will pour "a significant amount" of his own money towards the Yes campaign for same-sex marriage.
The high-profile gay business leader says marriage equality, however, should not come down to a costly optional postal survey but should have been decided in parliament.
"If the High Court says it goes ahead, then we will be fully behind it," he said when asked about his intentions after unveiling Qantas' full-year profit on Friday.
"I will be devoting money to the campaign, a significant amount, because I'm passionate about it."
Same-sex marriage advocates have challenged the federal government's planned $122 million non-binding postal survey in the High Court.
Mr Joyce said that if people believe in respect and equality then they should vote yes.
He said he was proud to be an Australian citizen because "where else in the world can an openly gay Irish man become the CEO of one of the country's biggest brands".
But, he believes Australia has fallen behind on "progressive issues" due to past and current political leadership.
"We were the second country in the world to give women the right to vote (but) 22 countries have gone ahead of us on marriage equality," Mr Joyce said.
