CNN went to two areas of Melbourne, Victoria, where polls show strong support for -- and against -- legislative change.
We asked people how they'd be voting and why.
Here's what they said.
"I say no!" says taxi driver Wally Nagas, who's gesticulating wildly beside his car at a cab rank in the suburb of Broadmeadows, outside Melbourne, Australia.
"The Muslim doesn't accept it, the Christianity doesn't accept it and even the Jews, they don't accept it," the 64-year-old says. "No one in the Earth accepts it in a religion."
Nagas works in Broadmeadows, a working class suburb in the Melbourne electorate of Calwell, where 53% support same-sex marriage, according to an ABC poll of almost 800,000 nationwide conducted by Vote Compass
The area has a strong manufacturing industry, high amount of public housing and a diverse mix of ethnic and religious backgrounds.
Around 25 kilometers (15 miles) away, in the electorate of Melbourne Ports, the same survey showed 79% were in favor of same-sex marriage -- equal with Sydney, and the highest level of support in the country.
Port Melbourne is a beachside suburb within the electorate, which in recent years has transformed from a former industrial hub to a haven of expensive apartments, restaurants and cafes.
Inside the Broadmeadows shopping mall, Sarah Abdalamer, 24, said she was voting in favor of changing the law.
"I actually agree with it," said Abdalamer, a Muslim who works at a make-up stall in the shopping center and is studying civil engineering.
She lives with her parents in Roxburgh Park, a nearby suburb with a high concentration of Muslim families, and believes there should be equality for all.
"Why not?" she says, "Everyone should be free to make their own choices so I don't mind at all."
"I think my parents feel the same way," she adds, "but maybe they are more laid back than others in our community."
Walking past Abdalamer's stall was Billy Webb, who was still fuming about an angry Facebook exchange about same-sex marriage with a school teacher friend just a few hours before.
He's voting no, but is mortified by suggestions that it makes him a bad father to his four children.
"This teacher was saying 'by voting yes I'm teaching equality to my kids and, if I vote no, I don't show any of the kids those qualities.'
"So I wrote back 'I'm a bloody good parent and I'm voting no.'"
Webb said he was "very frustrated" at being accused of being homophobic and bigoted for voting against changing the law.
"It's just the way I was brought up, I'm a Catholic lad bought up a bit rough around the edges.
"I'm a bit old school but we were taught that way... Just don't have a go at me when I say no.
"There's even talk of bringing in transgender school uniforms. Come on man, what's going on with society? It's getting bad."
Advertisements for the "no" campaign were released in the early weeks of voting, focusing on gender identity and a parent's right to teach their child about gender norms.
Campaigns in favor of a "yes" vote have largely focused on personal stories of same-sex couples and positive slogans such as "vote yes for love."
Both sides have been accused of forcing unwanted messages on the public, either through skywriting campaigns
(no), or mass unsolicited text messages (yes).
In Port Melbourne, Phillip Coulton, 64, said he believes the controversial advertising tactics should have been banned during the process.
"I see all the divisive stuff on TV and social media and think 'is this really necessary?' I believe it shouldn't have been allowed."
Coulton, who is retired, is voting yes but admits that even in Port Melbourne, where "yes" support is high, he has engaged in awkward debate with close friends who are voting "no. "
"I've found some of my friends are worried what the next step will be.
"Most of them are not worried about legalizing same sex marriage itself. They are more worried about what is going to happen afterwards in the future."
Hairdresser Tony Codespoti, 47, said, for him, the decision was easy.
"Of course, it's a yes, isn't everyone voting yes mainly?" he asked, but expressed annoyance the question was even being put to the public.
"We shouldn't even be having this postal survey, the politicians should do their jobs, that's what we are paying them for.
"Why are we spending all this money on this? This should have been sorted a while ago."
A number of Western countries have already changed the law to allow gay marriage, including the US, Canada and New Zealand.
Many are confused why it has taken Australia so long -- and why it's costing so much, around $122 million Australian ($96 million).
The government had intended to hold a compulsory national vote, or plebiscite, in February this year.
But after fierce objection from LGBT groups -- who did not want a popular vote to decide what they see as an issue of equality -- opposition parties blocked the proposed plebiscite in the Senate.
The government then decided to hold a postal survey which doesn't need legislation to be passed.
Walking down Bay Street in Port Melbourne with her husband Rod, Sylvia Hall said she had just sent off their forms. The retired couple is voting yes.
"I feel very strongly there should be equality for everyone, but it's not going to change anything for religions. They won't be forced to conduct same-sex marriages if they don't want to. They have their own internal laws."
Back in Broadmeadows, Georgia Vergiris, said she was too shy to speak to CNN at first when approached about her views.
But she later changed her mind, saying she felt an obligation to speak as she was "particularly concerned for future family structures."
The 33-year-old Muslim, who home-schools her three children, said she wasn't surprised the support for same-sex marriage was low in her electorate.
"Here there is great importance of the family unit and traditional structures," she said.
"And I believe children have the right to a relationship with both their biological parents so I don't think same-sex marriage should be further promoted in society.
"The family unit is the basis of society, I feel."
Given the emphasis on what the vote means for the future, whichever way it goes, many believe that it's unfair the views of the younger generation aren't being heard.
Only those aged 18 and over are eligible to vote.
Sharni Lee, 17, a student from Broadmeadows said she wanted to vote to send a message.
"I wish I could vote so I could prove the point that it's not fair that others can have the choice to marry but being gay you can't," she said.
"How is it a free country if people can't love who they want?"
The result is due on November 15.