Brown, who will also resign from the Senate, made the shock announcement to his colleagues this morning at 10am AEST.

“I am sad to leave but happy to go. It is good knowing that the Greens have such a depth of talent and experience lined up for leadership – I could only dream about that a decade ago,” Senator Brown said.

“It is prime time to hand over the reins.”

In a statement, Brown thanked his colleagues and the 1.7 million Australian voters who elected the Greens.

He also mentioned he was looking forward to observing progress from the sidelines while the Greens pushed for further reforms.

"Our policies for fairly taxing the resources boom and carbon polluters, uniquely enable the Greens to fund a national disabilities insurance scheme, the Gonski education reforms, Denticare, renewable energy businesses, as well as progress on High Speed Rail linking our major cities," he said.

Greens deputy leader Christine Milne has reportedly tweeted that she has been elected the new Greens leader.

Brown has called the Governor-General, the Prime Minister and the Leader of the Tasmanian Greens to inform them of his resignation.

Brown has not made many friends in Australia’s mining sector as leader of the Greens due to his persistent calls to expand the Minerals Resource Rent Tax beyond coal and iron ore to include gold and uranium.

This week, Brown cried foul over news the Australian Security Intelligence Organisation was monitoring environmental groups which target the coal industry.

Brown reportedly condemned the “deployment of ASIO as a political weapon” against “peaceful” protests.

This article first appeared in ILN's sister publication MiningNews.net,/i>