The Turnbull government has been plunged into turmoil and will head to a snap by-election after the High Court ruled Deputy Prime Minister Barnaby Joyce and four other MPs caught in the dual citizenship saga were disqualified from federal parliament.

The ejection of the Nationals leader means the government will lose its one-seat majority in the House of Representatives and likely embolden Labor, which has threatened to cause chaos and confusion if Mr Joyce’s election is deemed invalid.

Independent senator Nick Xenophon and former Nationals cabinet minister Matthew Canavan have been found eligible to sit in parliament.

Nationals deputy leader Fiona Nash, One Nation’s Malcom Roberts and former Greens senators Larissa Waters and Scott Ludlam have also been disqualified.

The parliament referred the elections of the “citizenship seven” to the High Court after questions emerged about their dual nationality.

Under section 44 of the Constitution, any person who is “a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power” is incapable of being chosen or of sitting as an MP.

Mr Ludlam triggered the dual citizenship fiasco after being told in July he was a New Zealander at the time of last year’s election.

The revelation prompted other parliamentarians, who faced weeks of questioning by the media, to make inquiries about their own status, leading to the referral of seven MPs.

The government argued Mr Joyce, Senators Nash, Canavan and Xenophon and Ms Waters should not be disqualified because they were Australian-born and unknowingly gained citizenship by descent.

In the case of Ms Waters, who was born in Canada, the government said she effectively became Australian-born when her birth was registered with Australian authorities.

But the government said Senator Roberts and Mr Ludlam should be found ineligible because they had some knowledge of their dual citizenship, as they were born overseas and migrated to Australia.

Only those who “voluntarily obtained or retained” their foreign citizenship should have their elections ruled invalid, the Solicitor-General Stephen Donaghue argued.

Tony Windsor, represented by former solicitor-general Justin Gleeson, argued that allowing Mr Joyce to keep his seat would result in “radical instability” and he should be disqualified for being a Kiwi when he nominated for the 2016 election.