The legislation was introduced by the government but voted down by the Labour opposition, the Greens and Nick Xenophon Team (NXT), who claimed the public vote at more than 120 million Australian dollars ($95 million) was an expensive waste of time.
They called for a free vote in Parliament to decide the issue.
The government earlier this week said if the bill was voted down in the Senate, then a voluntary non-binding postal vote would occur -- also at a cost of almost $100 million, ABC reported.
Because a postal vote is not required to pass through the Parliament, it will be going ahead from September, Prime Minister Malcolm Turnbull said.
In voting down the plebiscite bill, Deputy Opposition Leader Tanya Plibersek wondered why the government was content in spending so much money on a non-binding vote, which would still go to Parliament even if the people vote "yes".
"Is the Prime Minister aware that the 122 million Australian dollars he is wasting on his voluntary, non-binding postal plebiscite could instead fund over 1,800 aged care places or support over 2.7 million bulk-billed (doctor visits)?" Plibersek said.
Turnbull in a response said he was merely following through on his promise taken to the last federal election, which was the plebiscite.
"The government is giving every Australian a say on the issue of marriage, because we promised to do so, and we keep our promises," Turnbull said.
While the voluntary non-binding postal vote will not require approval from the Parliament, the government has one more hurdle to avoid -- same-sex marriage advocates and independent MP Andrew Wilkie have said they would challenge the misuse of public money.
Speaking in Parliament on Wednesday, Wilkie said it was frightening that the government was attempting to "bypass the Parliament and somehow authorise the expenditure of more than 100 million Australian dollars of taxpayer funds".
"This is a democracy, this is a country governed by the rule of law," he said.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
About VDC
Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.