Thursday was set to be a historic day for gay marriage advocates in Australia, with same-sex marriage expected to pass in the late afternoon.
The 33-year-old primary school teacher responded "yes", which was recorded in the official parliamentary record.
Four members of the House of Representatives voted against the bill.
The bill passed the Senate last week with 43 votes to 12, with Labor Senator Penny Wong reaching to hug Liberal Senator Dean Smith afterwards.
Several government MPs, including Prime Minister Malcolm Turnbull, have said they will support or at least consider changes to be put forward by their conservative colleagues - namely Andrew Hastie and Michael Sukkar. When the Attorney-General ratifies the law, same-sex marriage will finally be legal.
It will become law after being approved without amendments.
Not all speeches backed gay marriage, however.
"We must not fail to recognize that there is honest, heartfelt anxiety about the bill's impact on religious freedom", Turnbull said.
Further debate on amendments delayed the vote until almost 6pm tonight.
The government has appointed a panel to examine how to safeguard religious freedoms once gay marriage was a reality in Australia. Nearly 80 percent of Australia's registered voters took part in the two-month survey.
The only potential obstacle to the law passing on Thursday would be if marriage equality opponents managed to amend the legislation.