BOB Brown has resigned as leader of the Australian Greens parliamentary party.
He told his party colleagues of his decision morning.
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"I am sad to leave but happy to go," Senator Brown said in a statement.
"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."
He thanked his nine colleagues and the 1.7 million voters who supported the Greens in 2010.
"They have made each Green year in this parliament better than the year before - though the best is yet to come," he said.
Senator Brown advised the governor-general, Prime Minister Julia Gillard and the leader of the Tasmanian Greens of his decision.
He said he'll also resign from parliament when his Tasmanian replacement is available in June.
In addition, the party's deputy leader Christine Milne has tweeted that she's been elected the new leader.