Governor General Peter Cosgrove has given Royal Assent to the same-sex marriage bill and passed it into law.
The Governor General has signed the law to legalise same-sex marriage this morning, completing the legal process and formally changing the Marriage Act.
The Royal Assent is a final step before any bill can pass into law, and comes following the historic vote in the parliament on Thursday.
"It is now part of Australian law," an elated Mr Turnbull said.
“It is a big Australian hug for all same-sex couples,” Prime Minister Malcolm Turnbull told Channel Nine on Friday morning, in a string of media interviews.
“We love and respect you. Now go out there and get married,” he said.
Mr Turnbull travelled to Government House for the Royal Assent of the bill on Friday morning.
New same-sex weddings will not happen in Australia until the second week of January because same-sex couples will still need to lodge a Notice of Intended Marriage, which must be completed a month before the wedding.
At midnight tonight when the new law takes complete effect, the unions of thousands of same-sex couples living in Australia who were married overseas will be recognised under Australian law.
The ACT government, meanwhile, has promised to waive the marriage certificate fees for around 80 couples who were married when the territory briefly legalised same-sex marriage in 2013.
The bill to legalise same-sex marriage passed the House of Representatives on Thursday with an overwhelming majority.
Only four MPs voted no: Independent Bob Katter and Liberals David Littleproud, Keith Pitt and Russell Broadbent.
Many conservatives who opposed same-sex marriage either abstained or voted in favour of the bill to reflect the views of their local electorates, after a national postal survey found 61.6 per cent of Australian voters supported the change.