Greens Senator Scott Ludlam resigns over dual Kiwi citizenship

Greens Senator Scott Ludlam has resigned in a shock move on Friday afternoon.

"Recently it was brought to my attention that I hold dual citizenship of Australia and New Zealand. Under Section 44 of the Australian constitution I am therefore ineligible to hold elected office in the Federal Parliament," he said in a statement.

"I apologise unreservedly for this mistake. This was my error, something I should have checked when I first nominated for preselection in 2006. I have no wish to draw out the uncertainty or create a lengthy legal dispute, particularly when the Constitution is so clear.

"I am resigning as Senator for Western Australia and Co-Deputy Leader of the Australian Greens, effective today."

Mr Ludlam said he was devastated that a decade old "ridiculous oversight" had cost him his seat.

The Greens' deputy leader's resignation comes after the High Court ruled two other Senators ineligible, and amid a Labor Party challenge to Nationals MP and Assistant Health Minister David Gillespie's eligibility to run for office.

Family First's Bob Day lost his senate seat over a conflict of interest issue earlier in the year while One Nation lost WA Senator Rod Culleton to a High Court challenge over his right to stand.

Greens leader Richard Di Natale said he was devastated by the loss of Ludlam.

"Scott's decision today to deal with this issue directly and immediately shows his absolute integrity and character," Dr Di Natale said.

"In the coming days and weeks we will finalise what this means in terms of Scott's vacated seat. In the meantime, let's reflect on the tremendous contribution that Scott has made to this nation and to the Greens".

Ludlam was born in Palmerston North in New Zealand but left the country with his family when aged just three.

He settled in Australia just before he turned nine and became a citizen while a teenager. He never officially renounced his New Zealand citizenship.