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Christine Milne has resigned as leader of the Australian Greens.

She was replaced by Victorian Senator Richard Di Natale, a former GP and AFL footballer, following a meeting of the party room in Canberra. Di Natale was elected unopposed as leader, and will have senators Larissa Waters and Scott Ludlam as joint deputy leaders.

Milne was leader since 2012. She’s leaving the party with primary vote support at 12% in the latest Newspoll, down from a high of 14% last September.

Among the first challenges for Di Natale will be the Greens’ approach to working with the Abbott government. The Greens, who command 10 votes in the fractured Senate, have played a central role in frustrating the Coalition’s agenda.

Milne is a senator for Tasmania, just like her predecessor Bob Brown. They were both part of the protests against the Franklin Dam in 1983 as part of the Tasmanian Wilderness Society. Milne was arrested along with Brown at the protests, a landmark event in environmental activism in Australia. She entered politics in 1989 as a Tasmanian MP, off the back of being an activist against plans for a pulp mill in her hometown, Wesley Vale. Milne even managed to recruit then-environment minister and ALP heavyweight Graham Richardson to the anti-mill cause.

She was the first female Green in parliament, alongside fellow activist Di Hollister and the party held the balance of power in Tasmania at the time.

In 1993, Milne became the first woman to lead a political party in Tasmania, when Brown left for federal politics. She is the only Australian woman to lead both state and national political parties. Her move to the federal Senate in 2004 saw her become deputy leader in 2008, then Brown’s replacement in 2012.

A shift to a younger leader not associated with that era in Tasmania would mark a generational handover for the Greens and broaden the party’s mainland appeal.

Milne, who will not contest the next election, announced her decision on Twitter.

Feeling optimistic, proud & sad to announce I’m not contesting 2016 election, and so I resign as Leader of Australian Greens — Christine Milne (@senatormilne) May 6, 2015

In a statement, she said: “I have achieved what I set out to achieve when I took over the leadership. The Greens have gone from strength to strength with solid election results and a growing, engaged party membership.

“I promised a more cabinet-style, collaborative approach to leadership. I am so proud of the way that my colleagues have responded. We are a strong, capable, visionary Greens team.”

She said the decision to resign was “one I made with my family. After 25 years in politics, I am looking forward to spending more time in my beautiful home state of Tasmania, with friends and family, and especially as I am soon to be a grandmother.”

Under Milne’s leadership the Greens have been instrumental in blocking key legislation in the Senate, including the higher education reforms introduced last year in the Abbott government’s first budget.

The Coalition, however, repealed a treasured plank of Green policy when it rescinded the carbon tax, with support in the Senate from Clive Palmer’s Palmer United Party.

Milne sent a letter to Greens supporters this morning, saying that in her time in federal parliament, “we delivered a world-leading legislative package to price pollution – with an emissions trading scheme that worked and made the big polluters pay for their pollution, the biodiversity fund and $10 billion for the Clean Energy Finance Corporation. I was proud of our achievements then and I remain proud of them now. The repeal of the carbon price was the last stand of the vanquished. The community is now leaving the old parties behind in the fossil-fool age and getting on with realising the clean energy jobs of the future.”

The Greens currently have 10 Senators in the Upper House, including Milne, and Bandt is the single representative in the House of Representatives.

Prime minister Tony Abbott paid tribute to his political foe.

“We come from very different political traditions, but I respect Christine Milne… It takes a great deal of commitment and patriotism to offer to serve in the parliament, to serve at senior levels… it’s a testament to her commitment to Australia,” he said.

“We’ve always had good and cordial relations. I understand she’s soon to be a grandmother and that’s a marvellous time for any individual, and I wish her well in her future.”

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