The government said a non-binding ballot, or plebiscite, was the quickest way to amend the Marriage Act..
Same-sex couples can have civil unions or registered relationships in most Australian states but they are not considered married under national law
Opinion polls indicate that most Australians support same-sex marriage.
However opposition parties and many supporters of same-sex marriage argued a plebiscite would be expensive and could unleash a divisive campaign.
Instead, they say parliament should make the decision itself.