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Only four MPs in the lower house voted against a private bill today, just over a week after it was agreed to by the Senate.
It went through unchanged, despite a push from conservative politicians for additional exemptions - including for religious organisations, civil celebrants and Defence chaplains.
Prime Minister Malcolm Turnbull told parliament, just after a round of applause across the chamber and in the public gallery, the legal change belonged to all Australians.
"What a day! What a day for love, for equality, for respect. Australia has done it," he said.
"It's time for more marriages, more commitment, more love, more respect."
Labor leader Bill Shorten said the new law spoke for a modern Australia, "inclusive and fair".
"When this law is passed, we should declare we are no longer a nation of people who voted no, or people who voted yes - we are simply Australians one and all," he said.
Both major parties had given their members a free vote on the issue.
More than 120 MPs spoke during nearly 24 hours of debate on the bill, which was sponsored by gay Liberal senator Dean Smith and backed by colleagues Warren Entsch, Trent Zimmerman, Tim Wilson and Trevor Evans.
Former prime minister Tony Abbott tried to effectively kill off the legislation with an amendment that would stop its progress, but failed.
Treasurer Scott Morrison, junior ministers Michael Sukkar and Alex Hawke, and backbenchers Andrew Hastie, Andrew Broad and Sarah Henderson, were also unsuccessful in trying to change the bill, as was Greens MP Adam Bandt.
"It's time to pop the bubbly ... because love has won," Mr Bandt said.
The legislation will become law as soon as it is granted royal assent by the Governor-General.