South Australian senator Skye Kakoschke-Moore has announced she will resign from the Senate after she discovered she obtained British citizenship through her mother.
The Nick Xenophon Team member's mother was born in Singapore in 1957 to British parents.
Her mother migrated to Australia with her family in 1970 and Skye was born in Darwin in 1985.
She said she had previously sought advice about whether she was a dual citizen, but it was incorrect.
"As a 12-year-old while I was living in Oman, my father made inquiries with the British embassy there to determine whether I was eligible for a British passport," she said.
"We were advised that I was not eligible for a passport because I was not eligible for British citizenship.
"We had no reason to doubt that this advice was incorrect."
Senator Kakoschke-Moore said she sought clarification from the UK Home Office last Friday as part of the citizenship disclosure regime announced by the Prime Minister.
"Their advice was extremely surprising to me," she said.
"They advised that my mother was born in the former colony of Singapore before independence.
"This gave her citizenship of the United Kingdom and colonies under section 4 of the British nationality act 1948."
When Singapore attained independence, Senator Kakoschke-Moore's mother subsequently obtained the right to live in the UK.
"She was therefore able to pass her citizenship to any children born outside of the UK," Senator Kakoschke-Moore said.
"I am therefore a British citizen."
She said she did not believe she was a dual citizen until Friday and that all information available online indicated she was not a dual citizen.
'This isn't the end of my career'
Senator Kakoschke-Moore said she wanted to return to Federal Parliament at some stage, but ruled out running for a seat in the South Australian Parliament.
"I have always loved the Senate, that's where my passion is and at this stage, that is where my ambitions lie," she said.
In an emotional speech, she said she was proud of her work on the Defence Abuse Response Taskforce and with veterans.
She also introduced legislation to make it illegal for predators who lie about their age to children to make attempts to meet them, known as Carly's law.
"I'm driven by people and I will not risk losing my humanity by forgetting that," she said.
"I have unfinished business as far as I'm concerned in terms of advancing our political agenda.
"This will not be the end of my political career."
Kakoschke-Moore's replacement in the Senate unclear
In any recount of the state Senate vote, there is debate over whether former NXT candidate Tim Storer could take Senator Kakoschke-Moore's position.
Last month, the party's founder Nick Xenophon named his senior advisor Rex Patrick as his replacement in the Upper House.
Mr Storer objected to that move, arguing the position was rightly his.
However, the South Australian State Parliament confirmed now-Senator Patrick as the party's next representative in Canberra.
Mr Xenophon described Mr Storer as "a good bloke" despite the falling out, but said there were issues with him joining the Senate because he is no longer a member of the party.
"Our initial advice is that there are some important legal issues and it is unchartered legal territory," Mr Xenophon said.
Mr Xenophon was asked whether he was suggesting he wanted his party to be able to pick Senator Kakoschke-Moore's place instead.
"That's one of the arguments but it's still early days," he said.
"Other than to say the initial legal advice from the same legal team that represented me in the High Court successfully is that there are some important legal principles that have not yet been tested.
"To say anything more than that would be mere speculation."