Deputy Prime Minister Barnaby Joyce has told parliament he may be a citizen of New Zealand.
Mr Joyce told parliament on Monday the New Zealand High Commission had contacted him last Thursday with the "shocking" information.
He has referred himself to the High Court after making the stunning announcement.
"On the basis of preliminary advice from their department of internal affairs - which had received inquiries from the New Zealand Labor Party - they considered I may be a citizen by descent of New Zealand," Mr Joyce said.
Australia’s constitution bars dual citizens from eligibility for elected office unless they can show they have taken legitimate steps to sever foreign ties.
It's understood Mr Joyce could be a New Zealand citizen by descent as his father was born in the country and came to Australia in 1947.
However, Mr Joyce was born in Tamworth and says he has always considered himself an Australian.
"My father was born in New Zealand and came to Australia in 1947 as a British subject. In fact we were all British subjects at that time," he said.
"The concept of New Zealand-Australian citizens was not created until 1948.
"Neither my parents nor I have ever applied to register me as a New Zealand citizen. The New Zealand government has no register recognising me as a New Zealand citizen."
Mr Joyce won't be stepping aside from cabinet, remaining the Deputy Prime Minister and a minister for his portfolios.
If Mr Joyce is found to be ineligible, the government - which holds a one-seat majority in the lower house - would be forced into a by-election.
Mr Joyce is the fifth person to be caught up in the dual-citizenship saga in recent weeks.
One Nation senator Malcolm Roberts, former resources minister Matt Canavan and Greens senators Scott Ludlam and Larissa Waters have in recent weeks announced their dual-citizenships.
Three weeks ago, Mr Canavan quit parliament because is a dual citizen of Italy.
Mr Joyce came out in defence of the former minister last month and stumbled over his own citizenship when answering questions over whether he might have British citizenship due to his English grandmother.
He also took over the resources portfolio from Mr Canavan.
Mr Ludlam also resigned from federal parliament after admitting he holds a dual-citizenship for New Zealand.
Ms Waters, former deputy Greens leader, quit just a week before Mr Canavan after realising she holds a dual-citizenship because she was born in Canada.
Just last week, Senator Roberts was referred to the High Court by his party for a decision on whether he was a dual British and Australian citizen when he nominated for Parliament.
He claimed to have denounced his British citizenshship before being elected.