The Australian government was thrown into turmoil Friday after losing its one-seat majority with the nation's deputy prime minister kicked out of parliament over his dual citizenship.

Barnaby Joyce was among seven politicians embroiled in a crisis after falling afoul of a previously obscure constitutional rule that bars dual citizens from sitting in parliament.

The High Court ruled he was ineligible, meaning a by-election for his lower house seat of New England in New South Wales state will be held on December 2.

The court move reintroduced uncertainty into a political landscape that has been turbulent in recent years, with four different prime ministers serving since 2013.

"The decision of the court today is clearly not the outcome we were hoping for but the business of government goes on," Prime Minister Malcolm Turnbull said in Canberra after the ruling was handed down.

Joyce, the leader of the rural-based National Party, is Australian-born but found out in August he automatically acquired New Zealand citizenship through his father.

He told reporters in Tamworth, a city in his New England seat, that he was "always prepared for this outcome".

"I had no reason to believe that, you know, I was a citizen of any other country that Australia. That is the way it is... Now I am going to make sure that I don't cry in my beer."

The 50-year-old has since renounced his New Zealand citizenship, allowing him to run in the by-election.

- Constitution out of step? -

Independent MP Cathy McGowan said in a statement she would "continue to supply confidence and support to the government", giving the coalition room to breathe in the lower House of Representatives.

The deputy's position is expected to be kept vacant ahead of the by-election, with Foreign Minister Julie Bishop set to take on the duties if Turnbull travels overseas, according to local media.

Turnbull is assuming Joyce's agriculture portfolio.

If Joyce loses the by-election, the coalition could keep ruling as a minority government if it receives the support of independent MPs on budget matters and on votes of no confidence.

Of the so-called "citizenship seven", only Nationals senator Matt Canavan and independent senator Nick Xenophon were cleared for parliament.

The others, who are also upper house senators -- the Nationals' Fiona Nash, the Greens' Larissa Waters and Scott Ludlam and One Nation's Malcolm Roberts -- were like Joyce also ruled ineligible.

Canavan, who left cabinet and his role as resources minister after finding his mother signed him up to Italian citizenship in his 20s, resumed the job after being sworn back in.

Xenophon is quitting the federal Senate and moving to state politics by running in South Australia's election early next year.

The dual citizenship rule was originally inserted into the 1901 constitution to ensure parliamentarians were loyal solely to Australia.

However, critics say it is out of step with the modern reality of the country, where 50 percent of the population are either foreign-born or the children of immigrants.

The government's solicitor-general had argued to the court that Joyce and four of the other seven had not breached Section 44 of the constitution as they were unaware of their overseas citizenship.

But in its judgement, the court ruled that "proof of a candidate's knowledge of his or her foreign citizenship status (or of facts that might put a candidate on inquiry as to the possibility that he or she is a foreign citizen) is not necessary to bring about the disqualifying operation".

"It is sufficient to say that in none of the references with which the court is concerned were candidates confronted by such obstacles to freeing themselves of their foreign ties."

Turnbull said he was referring the ruling to a parliamentary committee to consider whether there should be constitutional changes to reduce the risk of future breaches.

Source:AFP