Bill Shorten has bounced between highs and lows in opinion polling in the three years he has been the opposition leader in Australia.

He was elected leader of the center-left Labor Party after it lost office in elections in September 2013, and by September last year, the closely watched Newspoll ranked him as a more popular choice as prime minister than the incumbent Tony Abbott. A poll found Shorten was the preferred choice as prime minister for 41 percent of the respondents — a four point lead over the beleaguered Abbott.

That was a huge change from Shorten's first Newspoll as Labor leader in October 2013, which showed him trailing Abbott 28 percent to 47 percent. The Newspolls have margins of error less than 3 percentage points.

While Australians don't directly elect their prime ministers, they rarely vote for a party with a leader they don't consider up to the job, and many joked that Abbott had become the Labor Party's greatest asset, with Labor looking likely to return to power after a single three-year term in opposition.

But Shorten's personal standing in the opinion polls dropped later last September when the more progressive and charismatic Malcolm Turnbull replaced the socially conservative and polarizing Abbott as the leader of the ruling conservative Liberal Party and as prime minister.

Shorten's popularity tanked in December around the time a government inquiry found damning results about labor union corruption in Australia. A Newspoll that month showed he was the preferred choice as prime minister for just 14 percent of respondents, while 60 percent preferred Turnbull.

Shorten had testified about his time as a union official, and while the inquiry made no findings against him, there were questions left unanswered about what Shorten knew about union corruption. Shorten has denied any wrongdoing.

But Shorten's popularity, and that of his Labor party, has been rebounding this year as Turnbull's honeymoon with the public fades. While Shorten is still less popular than Turnbull, many observers agree that Labor's momentum was a major reason that Turnbull decided to call an early election.

Turnbull has been hovering at about 45 percent as preferred prime minister in May and June while Shorten has stayed at about 30 percent in Newspolls that are published every two weeks. The government and opposition are running neck and neck in opinion polls.

Before he became opposition leader, Shorten was a powerbroker and a minister in the former Labor government that ruled for a chaotic six years until 2013.

He became known as one of Labor's "faceless men" — powerbrokers who made backroom deals to bring down Labor Prime Minister Kevin Rudd in 2010 and then Prime Minister Julia Gillard in 2014.

The Sydney Morning Herald's political editor Pater Hatcher wrote recently that the 49-year-old had managed an image makeover.

Labor opposes the government's proposed tax cuts for big business and vows to put people first by increasing spending on health and education.

"Bill Shorten began the Labor leadership as a Faceless Man, but he has now completed the shift to become Everyman," Hartcher wrote.

"The former union leader and backroom dealer who plotted to remove two Labor leaders is now empathizing with anyone and promising money to everyone," Hartcher said.