Re Canavan; Re Ludlam; Re Waters; Re Roberts [No 2]; Re Joyce; Re Nash; Re Xenophon (commonly referred to as the "Citizenship Seven case") is a set of cases, heard together by the High Court of Australia sitting as the Court of Disputed Returns, arising from doubts as to the eligibility of a number of members of Parliament to be elected to Parliament because of section 44(i) of the Constitution.

[8] Section 44(i) was considered by the High Court in 1988, which held in Nile v Wood that it required an identified foreign power.

[9] Robert Wood was subsequently found to be invalidly elected because he was not an Australian citizen and the High Court declined to decide whether dual citizenship of Australia and the United Kingdom would disqualify a person.

As part of the judgment the majority of the court held that a dual citizen was disqualified by section 44(i) unless they had “taken reasonable steps” to renounce their other citizenship.

[11] During 2017, there arose seven instances of a possible breach of section 44(i), when over the course of several months, media revealed that seven federal parliamentarians appeared to be dual citizens.

On 25 July 2017, Canavan resigned from his positions of Minister for Resources and Northern Australia over doubts as to his eligibility to be a member of the parliament, after discovering that he was considered by the Italian authorities to be a citizen of Italy.

Canavan stated he was unaware of this until his mother was prompted to inform him following news of the resignation of two Greens senators holding dual citizenship.

[31] Barnaby Joyce was the National Party member of the House of Representatives for the seat of New England, New South Wales from 7 September 2013.

[12] Ludlam with his family had settled in Australia aged eight, and had previously assumed he lost his New Zealand citizenship when he was naturalised as an Australian citizen in his mid-teens.

Three days after the announcement from Nationals leader Joyce, on 17 August 2017, Nash revealed that she had British citizenship by descent through her Scottish father.

She had previously believed that she was solely an Australian citizen and that if she would have needed to take active steps before age 21 if she wished to gain Canadian citizenship.

[36] There were factual issues in relation to Roberts' state of mind and knowledge and Justice Patrick Keane was assigned to determine the facts to be considered by the full court.

Xenophon stated: "I've never had, never sought, never received citizenship of another country but out of an abundance of caution I wrote to the Greek embassy and Cypriot high commission saying essentially, 'I've never been a citizen, I don't want to be, so if there's any question that I could be, I renounce any rights to be'.

[1]: para 19  On that approach, it first affirmed the view taken in Sykes v Cleary that the question of eligibility is to be determined with reference to the point of nomination.

[1]: paras 141–5 At an earlier directions hearing, the Chief Justice had approved the Commonwealth's undertaking to pay the legal costs of all the parties and of Tony Windsor (intervening in the Joyce case).

[45] According to some legal opinions, more than 100 Turnbull government decisions are vulnerable to legal challenge as a result of Joyce and Nash being ineligible to be in Parliament, and consequently to be Ministers, with lawyers concluding there is a high likelihood that the work the pair had done over the previous year could end up before the courts, because of section 64 of the constitution, which requires Ministers to be members of Parliament.

Xenophon, who was found eligible had, whilst the case was before the High Court, resigned from the Senate to run for the South Australian Parliament.

Two of the ousted MPs – Joyce and Nash – were members of Cabinet, requiring a rearrangement of the Second Turnbull Ministry, which took place on the same day.

[49] Following the High Court's decision, three more Senators and an MP resigned as a result of holding citizenship of the United Kingdom: Stephen Parry,[50] Jacqui Lambie,[51] and Skye Kakoschke-Moore.

[53] The candidate determined by the special count to replace Nash, Hollie Hughes, was found by the High Court in Re Nash [No 2] to be ineligible under s. 44(iv) of the Constitution because subsequent to the election but before the special count she held an "office of profit under the Crown" as a part-time member of the Administrative Appeals Tribunal.