SYDNEY, Australia — When Malcolm Turnbull was sworn in on Tuesday, he did not only become Australia’s 29th prime minister — he also became its fourth in just over two years. His three immediate predecessors were ousted by their own parties, including Tony Abbott, who was forced out Monday in a leadership challenge led by Mr. Turnbull.
Now that Mr. Turnbull, a wealthy lawyer and former investment banker, has the country’s top job, his main challenge is clear, said Hugh White, an intelligence analyst who from 1985 to 1991 advised Prime Minister Bob Hawke and Defense Minister Kim Beazley.
With Australia’s next election less than a year away, the governing Liberal Party — which, despite its name, is conservative — rejected the deeply unpopular Mr. Abbott in favor of Mr. Turnbull, a comparatively centrist figure whose views on climate changeand other issues are more in line with Australian public opinion.
But Mr. Turnbull will have to lead not only the lawmakers in his own party — 44 of whom did not vote for him on Monday night, against 54 who did — but also a country where policy in recent years often seems to have been made on the run, and often in response to flagging opinion polls.
Australia’s current political turmoil dates from the Labor Party government of Kevin Rudd, who became prime minister in 2007.
Mr. Rudd was ousted in an internal party coup in 2010 and replaced by Julia Gillard, Australia’s first female prime minister. As Ms. Gillard’s poll numbers fell, the party reinstalled Mr. Rudd months before the election of 2013, which Mr. Abbott’s conservative coalition won.
Already a polarizing figure when he took office, Mr. Abbott’s popularity declined amid a slowing economy as he made a series of political missteps and alienated many voters with his strongly conservative stances and often abrasive style.
His combative manner contributed to his government’s inability to get major budget measures through the lower and upper houses of Parliament.
Proposed university overhauls, widely disliked by voters, stalled in Parliament, and a paid parental leave plan and a co-payment for visits to the doctor covered by Australia’s Medicare system were either amended or dropped by the government, which could not negotiate the passage of the legislation.
Bob Gregory, a professor of economics at Australian National University, said Mr. Turnbull’s task would be largely one of communication. “What Mr. Turnbull has to do is straightforward,” Mr. Gregory said. “He’s got to explain things. You’ve no idea how powerful that is.”
In his pitch for the job, Mr. Turnbull promised to consult with colleagues and the public more often, saying Australians need advocacy from their leader, and not slogans.
That will include managing the Liberals’ governing coalition with the smaller, more conservative National Party, which is unlikely to embrace attempts by Mr. Turnbull to move to the center.
Mr. Gregory said he expected few policy changes from Mr. Turnbull in the short term. Indeed, in his first session of Parliament as prime minister on Tuesday, Mr. Turnbull made it clear that on at least two issues over which he has criticized Mr. Abbott in the past — climate change and same-sex marriage — his predecessor’s policies would continue.
Mr. Turnbull, who once used an expletive to describe Mr. Abbott’s climate-change policies, said that carbon emissions reduction targets Mr. Abbott recently proposed, which have been criticized as inadequate by scientists and environmentalists, were “very substantial.”
And he reiterated that the question of legalizing same-sex marriage would be put to a public vote after the next election, a proposal of Mr. Abbott’s that his critics had called an attempt to dodge that issue by taking it out of Parliament. Mr. Turnbull — who, like most Australians but unlike Mr. Abbott, supports same-sex marriage — said last month that he would have voted to legalize it had Liberal Party members been allowed to stray from the party line on the issue.
John Hewson, a former Liberal Party leader, said climate change was the party’s biggest moral, social, political and economic challenge. He said that Mr. Turnbull would have to persuade more conservative members of his coalition to move further with him on dealing with the issue, toward which the Abbott government showed its firm attitude this summer by moving to halt government investment in wind farms and domestic-scale solar projects.
“There are not too many growth sectors in the economy,” Mr. Hewson said. “I never understood why they moved to close down renewables. Basically, what Mr. Abbott did resulted in a fall in investment in that sector of 80 to 90 percent and a loss of 15,000 jobs. Why would you do that when you’re looking for growth sectors to replace mining?”
Mr. Hewson said he hoped Mr. Turnbull would reverse the government’s lack of support for renewable energy projects, even if it could not change emissions targets before an international conference on climate change in Paris later this year.
“He has got great rhetoric,” Mr. Gregory said of Mr. Turnbull. “He won’t pull out a magical new agenda that isn’t there. But he will be able to fix things with a few words. He will make things happen.”
Mr. Turnbull became a nationally known lawyer during the 1980s, when he fought the British government’s attempt to stop the publication in Australia of a memoir by a former British intelligence agent. During the 1990s, he was a venture capitalist and head of the Goldman Sachs investment bank in Australia. In 1994, he bought a stake in the Internet service provider Ozemail, which he later sold for millions of dollars. First elected to Parliament in 2004, he is believed to be one of Australia’s richest lawmakers ever.
Still, he has often been dismissed as a “silvertail,” as Australians call an extremely rich person. He lives in a harborside mansion in the suburban Sydney district of Wentworth, one of Australia’s wealthiest. He attended an elite private school in Sydney, though he was a scholarship student and has said that his father struggled with his school fees.
Mr. White described Mr. Turnbull as a “terrifically passionate person” with a strong drive and a formidable intellect, especially where policy is concerned. “He came to politics late, and he is not an ideological warrior,” Mr. White said, characterizing the new prime minister as a foreign policy buff and deeply engaged on the question of China’s changing role in the region and its relationship with the United States.
“Mr. Turnbull has a strong record for making stuff happen,” Mr. White said. “There is hope that he will be better placed than his predecessors at running a good government.”