The High Court has ruled Deputy Prime Minister Barnaby Joyce ineligible to sit in Parliament due to his dual citizenship.
The result will spark a byelection in the NSW seat of New England, putting the Turnbull government's razor-thin parliamentary majority at risk.
Mr Joyce referred himself to the court on August 14 after learning he had inherited New Zealand citizenship from his father James. Dual citizens are constitutionally prohibited from serving in Federal Parliament.
Mr Joyce stayed in cabinet while the court considered his case, citing legal advice that he would be safe.
He is one of five federal MPs knocked out by the court.
Deputy Nationals leader Fiona Nash is also among them, given her British dual citizenship. Her seat is set to go to the next person on the Coalition's NSW Senate ticket.
Fellow National and former cabinet minister Matt Canavan survived the court's judgement, despite doubts about whether he had Italian citizenship.
One Nation's Malcolm Roberts has also been disqualified. Born in India to a Welsh father, he did not renounce his British citizenship until well after last year's election. He is set to be replaced by the next on the One Nation ticket, Fraser Anning.
Former Greens senators Scott Ludlam and Larissa Waters - both of whom have already resigned from Parliament - were also ruled ineligible.
Crossbencher Nick Xenophon was also ruled safe, but he has already announced he would leave federal politics to run for South Australian Parliament, regardless of the court's decision.
All the court's rulings were unanimous.
The court said it was adhering to the "ordinary textual meaning" of section 44 of the constitution in finding Mr Joyce and the four senators ineligible.
Other interpretations of section 44 - put by government lawyers during hearings earlier this month - were all subject to an "implied mental element". Effectively, the court found ignorance of one's citizenship status was no excuse.
"Neither Senator Canavan nor Senator Xenophon was found to be a citizen of a foreign power, or entitled to the rights and privileges of a citizen of a foreign power," the court said in its summary judgement.
The story Barnaby Joyce and four senators ruled ineligible in shock High Court ruling first appeared on The Land.