The court judgment will be handed down at 2.15pm AEDT in Canberra.
Joyce, cabinet colleague Fiona Nash, former minister Matt Canavan, former Greens senators Larissa Waters and Scott Ludlam, One Nation senator Malcolm Roberts and crossbencher Xenophon were all referred to the court over their dual citizenship.
Australia’s constitution bans anyone holding dual citizenship from sitting in parliament, in a section aimed at ensuring MPs do not hold split allegiances.
Nationals leader Joyce is widely expected to win a by-election in his regional NSW seat of New England but it will be a concern for the Government, which has held on to power by one seat since the 2016 election.
Tony Windsor, a former opponent of Joyce and a party to the court case, is weighing up whether to contest the seat he held from 2001 to 2013.
The Government told the court the phrase “is a subject or citizen … of a foreign power” should be seen to refer only to a person who has voluntarily obtained, or retained, that status.
Solicitor-General Stephen Donaghue argued it was reasonable that where a person had no knowledge they ever were a foreign citizen, they should not need to take any steps to renounce their citizenship.
Senator Xenophon, who found himself to have British citizenship by descent, will leave parliament whatever happens to contest the South Australian state election in March 2018.
Greens senators Larissa Waters and Scott Ludlam have already resigned from parliament over their dual citizenship by birth in Canada and New Zealand, respectively.
India-born One Nation senator Malcolm Roberts is expected to lose his position after being found by the High Court in September of not having properly renounced his UK citizenship by descent – through his Welsh father – at the time of his 2016 election nomination.
Joyce and senators Canavan, Nash and Xenophon were born in Australia but were made citizens by descent.
Legal experts have suggested six of the seven will be disqualified but Senator Xenophon’s slightly different situation will mean he retains his seat.
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