Greens leader Richard Di Natale has declared the minor party the "natural home of progressive, mainstream Australian voters".
He has been picked to lead the Australian Greens after Christine Milne announced she was stepping down from the position.
In a move that took just hours, the Greens announced the 44-year-old Dr Di Natale had been elected unopposed, with Larissa Waters and Scott Ludlam elected co-deputies.
"I think the debate on terrorism and refugees means that the multiculturalism issue needs a champion. And I'm going to be that champion."
Dr Natale, the son of Italian immigrants, grew up in Melbourne and worked as a general practitioner and public-health specialist before entering politics.
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He worked in Aboriginal health in the Northern Territory, on HIV prevention in India and in the drug-and-alcohol sector.
He says he does not come to the Greens leadership as an ideologue but his experience has taught him what government needs to do for people's wellbeing.
"It became pretty clear to me that, if you want to improve people's health, you've got to start looking at the things that make people sick. You've got to have a clean environment.
"You've got to have clean air and clean water. You've got to make sure that people have a roof over their head, that they've got a decent education, that they've got meaningful work and they've got a social safety net if they get into trouble. They are the ingredients of good health care, and I'm going to be champion for that.”
“We can afford decent health care. We should be expanding Medicare, we shouldn't be tearing it down. We should be bringing dental care into Medicare. They're the sort of things I'm going to fight for."
Dr Di Natale pointed to climate change as the most important issue to him, suggesting that, if it is not addressed successfully, every other issue becomes redundant.
But he made clear that health care is another critical matter he intends to focus on.
“We're being told we can't afford decent health care at the moment. We're being told that, if you can't afford to go and see a doctor, well, tough luck. That's not the sort of country we want to be.
“We can afford decent health care. We should be expanding Medicare, we shouldn't be tearing it down. We should be bringing dental care into Medicare. They're the sort of things I'm going to fight for."
Dr Di Natale made it clear, too, he has not forgotten those Italian roots.
"I'm a sort of product of the great Australian experiment called multiculturalism. I want to be a champion of multiculturalism in the parliament. It's taking a beating at the moment. I think the debate on terrorism and refugees means that the multiculturalism issue needs a champion. And I'm going to be that champion."
Watch the press conference by Christine Milne and Richard Di Natale:
Elected unopposed
It took just two hours for the Australian Greens to come up with their third leader in three years.
Senate one-termer Richard Di Natale was elected unopposed to replace Christine Milne who quit the leadership in a surprise 10.30am announcement to party colleagues at Parliament House on Wednesday.
Senator Milne's lower house deputy Adam Bandt was the casualty of a partyroom meeting concluding about 12.30pm, with senators Scott Ludlam and Larissa Waters chosen to share his role.
Adam Bandt, who had previously served as deputy, handed over the role to spend more time with family.
Senator Milne was the first woman to lead a political party in Tasmania and remains the only woman to have lead a political party at both state and national level.
"It is with a mix of optimism, pride, excitement and sadness that I am resigning the leadership and leaving the Senate," she said in a statement on Wednesday.
Party members have thanked Senator Milne, such as her upper house colleague Penny Wright, who remarked on her "integrity, courage, vision, heart".
Senator Milne was elected to the Senate in 2004 after a 15-year stint in the Tasmanian parliament. She rose to leader of the federal party in 2012 after its founder Bob Brown resigned.
Senator Milne said she had achieved what she set out to do when she took over the leadership.
"The Greens have gone from strength to strength with solid election results and a growing, engaged party membership," she said in a statement.
"I promised a more cabinet-style, collaborative approach to leadership."
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Senator Milne said she was leaving in place a strong, capable and visionary team.
She said she was looking forward to spending more time with her family including her new grandchild in "my beautiful home state of Tasmania".
But Senator Milne won't leave the political field entirely, promising to use her passion and experience to continue the fight for action on climate change.
Abbott praises Milne's 'commitment'
Prime Minister Tony Abbott has paid tribute to Senator Milne's "distinguished record".
Speaking to media in Perth, Mr Abbott said it took great deal of "commitment and patriotism" to offer to serve in the parliament.
"Even though we have far more often than not been on opposite sides of most political arguments, I respect her commitment," he said.
"We've always had good and cordial relations. I understand that she's soon to be a grandmother and that's a marvellous time for any individual.
"I wish her well in her future."
Treasurer Joe Hockey said he was surprised to hear Christine Milne has quit as leader of the Australian Greens.
"I'll be very interested to know why," he told reporters on Wednesday shortly after the surprise announcement.
In a plea to the new leader of the minor party, Mr Hockey said he hoped the Greens would see common sense on such measures as reintroduction of fuel excise indexation.
Meanwhile, Defence Minister Kevin Andrews has said the leader of the "freedom hating" party does not matter.
Bob Brown has said the Greens have a good group of candidates from which to choose a new leader.
The former Greens leader named Melbourne MP Adam Bandt, the current deputy leader, and Tasmanian senator Peter Whish-Wilson as possibilities.
Pyne accuses Greens of knifing Milne
But tonight Senior Liberal Christopher Pyne said the Greens can no longer claim the moral high ground after "knifing" former leader Christine Milne.
"They put their forebears in Che Guevara and Fidel Castro to shame today because this was a revolution that took less than an hour," the education minister told Sky News.
Mr Pyne compared the Greens to the Democrats, who he said started "looking sick" to the Australian public once they began "knifing" their leaders.
He qualified his claims by saying discontent had been bubbling within the minor party for some time, leading to Wednesday's "cold-blooded" and "ruthless" leadership change to Richard Di Natale.
"They like to lecture Labor and the Liberals about bad politics versus this lovely perfect politics the Greens would give.
"But what we've seen today is they're just the same as any other political party."
The life and political career of Christine Milne
- Born in Latrobe, Tasmania, the second daughter of dairy farmer parents.
- Came to public notice in 1983 when she was arrested and jailed during the campaign to save Tasmania's Franklin River.
- Prominent in a successful community campaign to prevent the construction of Wesley Vale pulp mill in late 1980s.
- First elected to the Tasmanian Parliament in 1989.
- In 1993, she became the first woman to lead a political party in Tasmania.
- Elected to the Senate in 2004
- Replaced Bob Brown as federal leader of the Australian Greens in April 2012.
- Resigned as leader on May 6, after deciding not to contest the next federal election due in late 2016.
With AAP.
