Shorten is up against incumbent Scott Morrison, the leader of the center-right Liberal Party, who has held the top post for less than a year.
If Shorten wins, he'll be Australia's sixth leader in a decade marred by party infighting and leadership coups.
Shorten, who is credited with bringing unity to the Labor party, has been campaigning under the slogan of "A fair go for Australia," his second attempt at becoming Prime Minister.
Although he's been Labor leader for almost six years -- the party's longest-serving leader in almost two decades -- he remains a relative unknown on the international scene.
Here are six things you need to know:
1. He got his start in the union movement
Although Shorten joined the Labor party at 17
, he cut his teeth in union politics. In 1994, he joined the Australian Workers' Union, straight out of studying law at Monash University in Melbourne, and worked for similar organizations for the next 23 years until he was elected to parliament.
"He was able to have a fight, but he was also able to compromise and negotiate, not out of weakness but out of strength, and have a good relationship with business leaders."
Shorten first came to national fame in 2006 when the Beaconsfield Mine in Tasmania collapsed and trapped two workers. He became the public face of the incident, liaising with and supporting the family and community.
2. He's seen as a prime ministerial assassin
As a powerful member of Labor's right-wing faction, Shorten was closely involved
in replacing then-Prime Minister Kevin Rudd in June 2010 and crowning Australia's first and only female leader, Julia Gillard.
He quickly gained a reputation for being a behind-the-scenes power broker, and the image was reinforced when he publicly supported Rudd's bid to remove Gillard three years later.
A poll conducted after he took over the Labor leadership at the end of 2013 showed just 34% of Australians
considered him "trustworthy."
3. He has some bold policies on tax and climate change
Shorten is promising to crack down on tax loopholes
used by multinational companies, introduce tax cuts
for low and middle-income Australians, and make large companies reveal their gender pay gaps
He's also promising "real action
" on climate change -- a contrast with the Liberal party, which has several prominent members who are climate change skeptics.
Under Shorten, Labor says it will create clean transport infrastructure, invest in renewable energy and aim to reduce pollution by 45% on 2005 levels by 2030.
"I just don't want my children to come and see flora and fauna, I want their children to come and see it, and future generations to see what makes Australia so special," Shorten said
earlier this month after holding a koala on the campaign trail.
4. He supports Australia becoming a republic
Australia's head of state is still the UK's Queen Elizabeth II -- but that could change under Shorten.
Shorten has previously promised to hold a plebiscite to gauge support for Australia becoming a republic with its own head of state. That would then be followed by a formal referendum. Becoming a republic is on Labor's policy books
"We can vote for a republic and still binge-watch 'The Crown' on Netflix," Shorten said
in 2017. "And we can vote for a republic without derailing the business of government, or the priorities of this nation."
5. He's been surrounded by strong women
Shorten has consistently ranked poorly in preferred Prime Minister polls. Australian media has described him as unlikeable.
But two women have helped humanize Shorten this campaign: his wife and his late mother.
While Shorten has struggled to inspire voters, his wife has been called "warm
" when accompanying him on the trail. If Shorten becomes Prime Minister, she has said she wants to use her platform to promote feminist causes.
"I think that I will always bang on about the things that are very unjust for women because they are still there," she told
site Future Women.
"I'm sure that everyone here and across Australia can understand why I'm happy to be known as Chloe Shorten's husband," Bill Shorten quipped
when he launched his party's campaign this month.
The couple have one child together, nine-year-old Clementine, while Chloe Shorten also has two children from her first marriage.
For Shorten, one of the most emotional moments of the campaign came after an article in local media
earlier this month, headlined "Mother of invention," accused him of omitting details about his mother's life.
He had said
previously that his mother had put her dreams of being a lawyer on hold to support her siblings, adding she was his inspiration. But the article pointed out that she had gone on to study law later in life.
The article was widely condemned and Shorten gave an emotional press conference denouncing it. "I'm glad she wasn't here today to read that rubbish," he told reporters
as he fought back tears. "My mum is the smartest woman I've ever known."
6. He loves a dad joke
Not only is Shorten a dad -- some say he's a bit of a dork.
After he danced
with locals on the Pacific island of Kiribati during a 2015 trip, social media users described his moves as "dorky
"The good news for me is I'm running for Prime Minister, not running for 'Dancing With The Stars'," he said afterwards.
He's also well known for his love of dad jokes -- although those have tailed off since 2016
"Once upon a time I thought denial was a river in Egypt -- it's actually the attitude of the Abbott government," he quipped
in 2014 about former Prime Minister Tony Abbott.
In 2016, when then-treasurer Morrison called out Shorten's ill-fitting suit, Shorten told The Project
: "I think the problem is that Australia's got an ill-fitting treasurer."