West Australian Greens senator Scott Ludlam has resigned from the Senate effective immediately after revealing he had recently learnt he remained a New Zealand citizen despite being naturalised as an Australian citizen as a child.

Ludlam, who was born in New Zealand and moved to Australia at the age of three, says he assumed his naturalisation removed his New Zealand citizenship, but that it had recently been drawn to his attention that he remained a New Zealand citizen. Under section 44 of the constitution, anyone who "is under any acknowledgement of allegiance, obedience, or adherence to a foreign power" cannot stand for parliament.