Australian Greens co-deputy leader Scott Ludlam is resigning from politics, after it emerged he holds dual citizenship of Australia and New Zealand.
Mr Ludlam, who is also the senator for Western Australia, recently discovered he is a citizen of both Australia and New Zealand.
The dual citizenship means under the Australian constitution he cannot legally be a member of the Australian Parliament.
"I am personally devastated to learn that an avoidable oversight a decade ago compels me to leave my colleagues, supporters and my wonderful team," Mr Ludlam said in a statement.
"This was my error, something I should have checked when I first nominated for preselection in 2006."
Mr Ludlam grew up in Palmerston North and left New Zealand when he was three.
Under the Australian constitution in section 44(i) election to public office is ruled out for: "Any person who is under any acknowledgement of allegiance obedience or adherence to a foreign power, or is a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power."
In New Zealand there is no rule that states that dual citizens are ineligible to run for Parliament. In order to run for election a candidate must be registered, be on the electoral roll and be a New Zealand citizen.
Former New Zealand Greens co-leader Russel Norman was born in Australia, he moved to New Zealand in 1997 and was elected to the Green party in 2008.