Greens senator Scott Ludlam has resigned from Parliament effective immediately after realising he is “ineligible to hold office” because he is a dual citizen of Australia and New Zealand.

The Western Australian Senator and Co-Deputy Leader of the Australian Greens announced his resignation on Friday afternoon, saying he was “personally devastated” about the discovery.

“Under Section 44 of the Australian constitution I am therefore ineligible to hold elected office in the Federal Parliament,” Senator Ludlam said in a statement.

Senator Ludlam was born in Palmerston North in New Zealand’s North Island and left the country as a three-year-old.

The revelation means his election to the Senate in 2007, 2013 and 2016 was invalid.

“I apologise unreservedly for this mistake. This was my error, something I should have checked when I first nominated for preselection in 2006,” he said on Friday.

“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 immediately.

“I am personally devastated to learn than an avoidable oversight a decade ago compels me to leave my colleagues, supporters and my wonderful team.”

Senator Ludlam thanked the Greens’ supporters for their support “through the challenges of the past year”.

“You are the people who entrusted me as your candidate and sent me to parliament, and you are the people who turned out in force as we fought an unprecedented by-election in 2014,” he said.

The 47-year-old explained that he settled in Australia not long before he turned nine and believed he had relinquished his New Zealand citizenship when he became naturalised.

“I was naturalised when I was in my mid-teens and assumed that was the end of my New Zealand citizenship,” he said.

“I’ve been incredibly fortunate to serve these past nine years in the Australian Senate. The scruffy kid who cut his teeth at the Jabiluka uranium blockade was honoured last week to speak in the United Nations plenary on the historic nuclear weapons ban. It’s not a bad way to go out.

“I’ll find a way to continue making a contribution in some different capacity, but thank you all for sharing this remarkable ride with me.”

Senator Ludlam was Greens spokesperson for Foreign Affairs, Defence and Veteran’s Affairs, International Aid and Development, Communications, Sustainable Cities, and Nuclear issues.

Greens Leader Richard Di Natale said he was “absolutely devastated” by the resignation.

“Scott’s decision today to deal with this issue directly and immediately shows his absolute integrity and character,” Senator Di Natale said in a statement.

“As a colleague, Scott has been an outstanding member of the Parliament and of the Greens.

“As a friend, one could not ask for anything more.”

Senator Di Natale said the Greens would finalise what this will mean in the coming days and weeks.

The next Greens candidate on the Senate ticket is 22-year-old Jordan Steele-John, who could be elected if he wants the position.

Mr Steele-John said if it came down to it, “I’d be happier putting the choice of candidate back into the hands of our party membership”.

Senators Larissa Waters, Adam Bandt, Sarah Hanson-Young and Lee Rhiannon all expressed their gratitude to Senator Ludlam.

Former Prime Minister Tony Abbott, who was born in the UK, on Friday shared evidence he had renounced his British citizenship.

His citizenship was renounced in October 1993, records show.

Robert Wood was elected as a Senator for the Nuclear Disarmament Party in 1987, but was later declared ineligible to sit by the High Court because he was not an Australian citizen at the time.

Earlier this year, South Australian Family First Senator Lucy Gichuhi faced a High Court challenge but was found to have been duly elected. Labor wanted to challenge her eligibility over questions on her Kenyan citizenship.

FYI rumour mongers: I renounced my UK citizenship in 1993 and here's the proof: pic.twitter.com/tHAeJeqo5T

— Tony Abbott (@HonTonyAbbott) July 14, 2017

Huge loss to the Parliament for my dear friend & co-deputy leader @SenatorLudlam to be leaving, but he will remain a remarkable campaigner

— Larissa Waters (@larissawaters) July 14, 2017

Scott & I started our political journey in the Senate together. A great Senator & wonderful activist. Damn it @SenatorLudlam we'll miss you

— 💚🌏 Sarah Hanson-Young (@sarahinthesen8) July 14, 2017

We will miss you, @SenatorLudlam, and your commitment to rooting out warmongers and making the world a more peaceful place ✌️

— Adam Bandt (@AdamBandt) July 14, 2017

For all issues Scott has brought exceptional insight and advanced many progressive causes. Pls continue to stir up trouble, Scott. https://t.co/ox1xCFUVZ0

— Lee Rhiannon (@leerhiannon) July 14, 2017