Malcolm Turnbull, an urbane former investment banker who supports marriage equality and action on climate change, was sworn in as Australia's 29th prime minister on Tuesday, a day after ousting longtime rival Tony Abbott in a party room coup.
Turnbull, a Rhodes Scholar who previously led the Australian Republican Movement, was sworn in by Governor General Sir Peter Cosgrove, the representative of Britain's Queen Elizabeth, Australia's head of state.
Turnbull's Liberal Party and its junior coalition partner the National Party won a landslide election in 2013 but Abbott was jettisoned by his party after a series of perceived policy missteps and destabilizing infighting.
"I'm filled with optimism and we will be setting out in the weeks ahead ... more of those foundations that will ensure our prosperity in the years ahead," Turnbull told reporters as he headed to parliament on Tuesday.
Abbott was deposed following months of opinion polls that showed his popularity with the public near rock bottom as Australia's $1.5 trillion economy struggles to cope with the end of a once-in-a-century mining boom.
Turnbull, toppled as leader of the conservative Liberal Party by Abbott in 2009, has consistently been seen as a preferred prime minister. However, his support for a carbon trading scheme, gay marriage and an Australian republic have made him unpopular with his party's right wing.
Turnbull is widely expected to overhaul the cabinet, with current Treasurer Joe Hockey, who has been battling a backlash against a deeply unpopular budget, likely to be replaced by Social Services Minister Scott Morrison.
Former Australian Prime Minister Tony Abbott speaks to the media at Parliament House in Canberra, September 15, 2015. Photo: Reuters/Matt Siegel
Defense Minister Kevin Andrews, who is overseeing a A$50 billion ($35.70 billion) submarine tender, is also expected to be replaced when Turnbull unveils his ministry later this week.
Foreign Minister Julie Bishop, who won the party room vote to retain her additional position as deputy prime minister, said she had spoken with international leaders overnight about the leadership change.
The opposition Labor Party was quick to label Turnbull a "multi-millionaire who lives in a pink mansion on Sydney Harbor" who was out of touch with everyday Australians.
The change of leaders is the latest sign of political instability in Australia, which has in recent years been convulsed by backroom machinations and party coups that have shaken public and business confidence in government.
Labor's Kevin Rudd, elected prime minister with a strong mandate in 2007, was deposed by his deputy, Julia Gillard, in 2010 amid the same sort of poll numbers that Abbott faced. Gillard was in turn deposed by Rudd ahead of elections won by Abbott in 2013.