SYDNEY — Malcolm Turnbull, set to become Australia’s next prime minister after winning a leadership challenge on Monday, is a millionaire former banker whose socially liberal views, such as support for gay marriage, are at odds with those of some of his fellow conservatives.

The 60-year-old, said to be worth upwards of A$100m ($71m), has led the right-wing Liberal Party before — serving as opposition leader for just more than a year from September 2008. He was dumped when he refused to abandon a trading scheme for carbon emissions meant to fight climate change, a policy many in his party rejected. His moderate views on social issues have made waves, including backing gay marriage, which is illegal. But he remains popular with business leaders because of his background in law, banking and communications.

Mr Turnbull, after defeating incumbent Prime Minister Tony Abbott 54-44 in a party room ballot, stressed he would lead a government that was consultative and collaborative and which would have a smarter style of leadership in a complex world.

“My firm belief is that to be a successful leader in 2015, perhaps at any time, you have to be able to bring people with you by respecting their intelligence in the manner you explain things,” Mr Turnbull said.

In some quarters he has a reputation for being arrogant, and his staggering wealth

puts him at risk of being criticised as out of touch with ordinary Australians.

But the witty and eloquent Mr Turnbull is an adept user of social media, and he may also be seen as the best hope of winning over swing voters who would otherwise side with the opposition Labour party.

In 2012 he admitted to the Sydney Morning Herald he was ambitious, but said: “I would not want to be prime minister of Australia at any price.”

Earlier on Monday he said electoral defeat was staring Mr Abbott in the face and change was needed “for our country’s sake, for the government’s sake, for the party’s sake”.

Mr Turnbull was raised by his father, after his mother left when he was in primary school, and he was educated at Sydney Grammar, helped by a scholarship.

A Rhodes scholar at Oxford, he worked as a journalist before turning to law, gaining prominence in the 1980s for successfully defending former spy unit MI5 agent Peter Wright against the British government in the “Spycatcher” trial.

He then became a merchant banker, and invested in technology startups, before entering public life by spearheading the push for Australia to break ties with British royalty and become a republic. The campaign was unsuccessful, but by October 2004 he had entered parliament and under Liberal prime minister John Howard rose to be environment minister.

When Mr Howard was swept from power in 2007, Mr Turnbull was not the first choice to lead the party, but was opposition leader within a year. After his subsequent loss of the Liberal leadership, which went to Mr Abbott by just one vote, Mr Turnbull at first contemplated resignation from politics.

He was persuaded to stay on, and as communications minister has worked hard to sell government policies.