Malcolm Turnbull was sworn in Tuesday as Australia's new prime minister, becoming the country's fourth leader in just over two years.
Turnbull emerged as leader of the Liberal Party following a surprise party vote late Monday that ousted Prime Minister Tony Abbott.
The 60-year-old ex-banker, lawyer and journalist told reporters he was "filled with optimism" as he headed for his swearing-in ceremony.
"This is a turn of events I did not expect, I have to tell you, but it's one that I'm privileged to undertake, and one that I'm certainly up to," said Turnbull.
Turnbull has vowed to oversee a less divisive government than the conservative Abbott, who on Tuesday pledged to make the leadership transition as smooth as possible.
"There will be no wrecking, no undermining, and no sniping. I have never leaked or back grounded against anyone and I certainly won't start now," Abbott said.
The outgoing leader also decried the "poll-driven panic" he said has produced a "revolving-door prime ministership" and a "febrile media culture" that he claims "rewards treachery."
Abbott, who was elected in September 2013, has seen his popularity ratings suffer in recent months, thanks in part to a series of internal leaks, unpopular budget cuts, and an inability to spur economic growth.
Turnbull differs from his predecessor on several key issues: most notably, he supports gay marriage and more stringent anti-pollution policies. Those differences are expected to be highlighted later this week when Turnbull announces his new cabinet.
The shakeup is expected to improve the chances of the Liberal Party, which faces a tough challenge from the opposition Labor Party in elections that are set for next year. Turnbull has for now ruled out early elections.