By his own admission, he only became a supporter of the cause in 2014. He may be the first openly gay Liberal MP in Federal Parliament, but Smith is also a staunch conservative (he is a big fan of the Queen). And is a devout Christian.

In a workplace where egos, shouting and outrageousness tend to get you ahead, Smith does not fit the mould. He chooses his words – and his actions – carefully.

And yet on Thursday morning it was Smith, the senator from Western Australia, who began debate in the Senate on a bill to legalise same-sex marriage in Australia. There have been many parliamentarians who have fought for the change over the past decade. But after 22 legislative attempts, Smith leads the bill that finally has a chance of success.

After the high emotion of Wednesday's announcement, where LGBTI Australians hugged, cried, partied and threw glitter, Smith calmly took to his feet in the Senate.

"On behalf of the gay, lesbian, transgender, bisexual and intersex Australians and their families, I say with humility and with gratitude, thank you," he said of the clear 61.6 per cent "yes" result.

"Yesterday we saw a glimpse of the country we all yearn for, a country that is fair-minded, generous and accepting."

Amid a debate that has been sidetracked by concerns about the rights of cake makers and wild claims about what kids will be taught at school, Smith offered his analysis of what the postal survey result means.

"There was an understanding by our fellow citizens that the life path for young gay or lesbian teenager or young adult is harder than their heterosexual brothers and sisters. Australians voted to make that path easier. It wasn't just a vote of acceptance, it was that deep loving embrace of a big family."

But there was a strong dose of "don't mess with me" running through the WA senator's considered words, as he pointedly noted that all states had returned a majority "yes" vote.

"The postal survey was a vote on amending the Marriage Act, full stop. Yes, there are other worthy debates about freedom of expression and living out our shared values, and yes, I will be a willing and enthusiastic participant in those debates. But those matters cannot be part of the Marriage Act."

Smith spoke of how, when he was a young man, he never believed he could work as a senior advisor to a prime minister because he was gay (John Howard proved him wrong).

He added that he never believed he would be accepted to Parliament because of the same reason.

But the steady flow of his monologue was suddenly broken when he got to the next line. For a second, the chamber worried the senator had lost a page of his speech. Or lost concentration.

He paused for a long moment. And his voice shook, just a little, as he fought to continue: "And I never believed the day would come when my relationship would be judged by my country to be as meaningful and valued as any other. The Australian people have proved me wrong."

Back in control, Smith lifted his head.

"Don't underestimate the Australian people."