Gay marriage campaigners including television star Magda Szubanski have gathered outside Parliament to celebrate as same-sex unions are about to be legalised.
More than 100 MPs had delivered speeches, many emotional, in the lead-up to the final vote with most in support of changes to the Marriage Act.
Media captionWill you marry me?
The House of Representatives is widely expected to vote to allow same-sex marriage across the nation.
The major parties want the legislation passed this week after a majority of Australian's endorsed change in a postal ballot last month.
But several lawmakers including Prime Minister Malcolm Turnbull intend to persist with amendments rejected by the Senate.
Liberal senator Dean Smith's bill will now become law after a day of cheers, tears and applause in the Lower House.
On Monday, the debate on the Marriage Amendment (Definition and Religious Freedoms) Bill 2017 kicked off in the House of Representatives. "The question though is we need to get the balances right in terms of the protections of those people who have fundamental beliefs based on religion or otherwise", he added. Dutton said none of his allies meant to delay gay marriage until those safeguards were decided.
The only potential obstacle to the law passing on Thursday would be if marriage equality opponents managed to amend the legislation.