Deputy prime minister Barnaby Joyce, Nationals senator Fiona Nash, former Greens senators Scott Ludlam and Larissa Waters, and One Nation senator Malcolm Roberts, have all been found to be ineligible to be elected to parliament for holding dual citizenships.
The High Court ruled on Friday that five of the so-called "Citizenship Seven" were ineligible under Section 44 of the constitution.
Independent senator Nick Xenophon and Nationals senator Matt Canavan were both found to be eligible.
There will be a by-election in the seat of New England as a result of the judgement. Prime minister Malcolm Turnbull said in a press conference on Friday that the by-election would be held on 2 December, and Joyce was "enthusiastic and ready to go" for it.
The prime minister will take on the responsibility for the agriculture and water portfolios while Joyce is out of parliament, and announced that Canavan would return to the ministry in his portfolio as minister for resources and northern Australia. Nash's regional communications responsibilities will go to communications minister Mitch Fifield.
The High Court's decision takes the government's majority in the House of Representatives from 76 to 75 (or 74 once the speaker is removed from the tally). Labor has 69 seats, and there are five cross-bench senators. Independent MP Cathy McGowan has guaranteed support the government on confidence motions while the by-election is underway.
Opposition leader Bill Shorten tweeted after the ruling that the country now had a "minority government"
Joyce broke the law and as a result, we now have a minority government. Turnbull should've stood him aside, terrible judgement once again.
Xenophon was in Senate Estimates at the time the judgement was handed down, but was told he was good to stay. He is planning to resign from the Senate regardless as he will run for the state parliament in South Australia next year.
Joyce, who said he would run in the by-election if he was selected by the Nationals as its candidate, jokingly asked if he could swap places with Xenophon.
"Nick, do you want to swap mate?"
.@Barnaby_Joyce asks @Nick_Xenophon if he wants to trade places, seeing as he is leaving federal parliament. MORE:… https://t.co/W7vqgqF468
An emotional One Nation leader Pauline Hanson said in a press conference that she was "devastated" that Roberts was ruled ineligible.
"I've lost a great man in Malcolm Roberts... I'm absolutely devastated," she said.
Hanson announced that Roberts would run for One Nation in the state seat of Ipswich in Queensland in the upcoming state election.
.@PaulineHansonOz: Federal parliament may have lost @SenatorMRoberts, but Qld has not lost him. MORE:… https://t.co/WQz2Df0qXq
Roberts refused to apologise for branding BuzzFeed News and others raising questions about his citizenship as liars, but admitted that the High Court has said he was wrong. He claimed, however, that the High Court did say he was "honest and genuine".
Roberts said he would speak more about the matter on a "fair and balanced" show tonight (likely either the Bolt Report or Paul Murray Live on Sky News).
Paul Murray infamously claimed that he had seen evidence from Roberts (that the former senator refused to show anyone else) that he had renounced his citizenship and it was "a million percent correct".
Greens leader Richard Di Natale said that Ludlam and Waters had acted with integrity by resigning as soon as they discovered their dual citizenship, and targeted Joyce, Nash and Roberts, who refused to resign but have now been found to be ineligible.
"If people are going to have faith in our democracy, then politicians need to start acting with integrity, with some decency and start taking responsibility for their actions," he said.
There is set to be a count back of the Senate votes for the senators ruled ineligible, meaning the people next down the ticket for each party will likely be elected in their place.
.@RichardDiNatale: Politicians have to start acting with integrity and decency for democracy to be supported. MORE:… https://t.co/sX2wsP5HiW
The High Court sat over three days earlier this month to hear the cases.
The court spent two weeks deliberating whether the dual citizenship held by the seven current and former politicians makes them ineligible to sit in parliament.
Section 44 of the Australian Constitution states that a person who "is under any acknowledgement of allegiance, obedience, or adherence to a foreign power, or is a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power" is ineligible to sit in, or be elected to, parliament.
The citizenship saga began on July 14 when former Greens senator Scott Ludlam resigned from parliament after discovering he was still a dual New Zealand citizen, having been born across the ditch.
His Australian Greens colleague Larissa Waters, who was born in Canada, resigned from the Senate days later.
Nationals senator Matt Canavan stood down as resources minister on July 25 after he initially claimed his mother had signed him up for Italian citizenship. He later said in court that he had in fact been an Italian citizen since the age of two. Canavan has stayed on as a backbench senator.
Deputy prime minister Barnaby Joyce revealed on August 14 he had inherited New Zealand citizenship from his father. Unlike Canavan he refused to step aside from his role as deputy PM and his ministerial duties.
Deputy Nationals leader Fiona Nash announced she was a British citizen, through her Scottish father, on August 17. Like Joyce she remained in cabinet.
One Nation senator Malcolm Roberts was referred to the High Court on August 9, after it was revealed he did not renounce his British citizenship until five months after he entered parliament. Roberts was born in India to a Welsh father.
South Australian senator Nick Xenophon rounds out the citizenship seven, with his peculiar form of dual British citizenship. Xenophon inherited the sub-class of citizenship from his father who was born in Cyprus when it was a British colony.
Sky News reported today that the government was considering changes to Australia's Citizenship Act designed to prevent issues with people unwittingly becoming dual citizens and thus being prevented from sitting in parliament in the future.