In 1990, George Turner, a Sydney-based barrister and independent Senate candidate, threatened High Court action against federal parliamentarians holding dual citizenship.

It provides thata person who "has any direct or indirect pecuniary interest in any agreement with the Public Service of the Commonwealth ... shall be incapable of being chosen or of sitting" as a member of Parliament.

[28][29] Senator Rodney Culleton, who had left Pauline Hanson's One Nation on 19 December 2016 to become an independent, had his eligibility to stand in the 2016 election challenged on two constitutional grounds.

Among the grounds of ineligibility provided in Section 44, a person cannot sit in either house of the Parliament if they are bankrupt or have been convicted of a criminal offence carrying a potential prison sentence of one year or more.

[30] This judgment was followed later on the same day by the High Court's decision that Culleton was ineligible owing to conviction for a criminal offence carrying a potential prison sentence of one year or more.

The Common Informers (Parliamentary Disqualifications) Act 1975 (Cth) has now provided otherwise, fixing the penalty at a total of $200 for any parliamentarian who has sat while ineligible in the past 12 months and $200 per sitting day after the suit is instituted.

[46] On 11 July 2018, Justice Gordon made orders in the High Court for the first time that judgment be entered for a plaintiff against defendants in a Common Informer action.

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

[127] On 6 September 2018, Waters was appointed to fill the casual vacancy caused by the resignation of her replacement, Andrew Bartlett, to contest the House of Representatives division of Brisbane.

[citation needed] 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.

[137] Doubts persisted about the status of Roberts' Indian citizenship after it was argued in the media that under a precedent set by the Supreme Court of India, he continued to be a 'presumed citizen' of the country.

[150] The High Court permitted Tony Windsor, the independent former MP who was defeated by Joyce for the Division of New England in the 2016 general election, to be joined as a "contradictor"[f] in the eligibility case.

Windsor expressed interest in running against Joyce in a resultant New England by-election, although the then-Deputy Prime Minister held the seat by a comfortable margin and his re-election was considered likely.

[66] On 27 October, in the Citizenship Seven Case, the High Court found that, as a foreign citizen, Nash had not been eligible to nominate; the replacements for all members declared to be disqualified would be determined by a countback.

He 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'.

[166][167] In the preliminary hearing on 12 October 2017, Chief Justice Susan Kiefel observed: "It is hardly necessary to say that the Court is aware of the need to give its answers to these references with or without reasons as soon as possible.

On 9 November 2017, Prime Minister Turnbull threatened to break with convention and use government-party numbers to secure a referral by the House of three Labor MPs: Justine Keay, Susan Lamb and Josh Wilson.

[197] On 28 November 2017, Prime Minister Malcolm Turnbull asked the Commonwealth Parliament's Joint Standing Committee on Electoral Matters (JSCEM) to conduct a new inquiry into the section, including the possibility of amendment.

[citation needed] It has been reported that Parry became aware of his possible dual citizenship status following the revelations involving Fiona Nash in August 2017, and had discussed the matter with cabinet member Mitch Fifield months earlier, who advised him not to raise those concerns publicly due to the belief that both Canavan and Joyce would be found to be eligible.

[201] On 2 November, Prime Minister and Liberal Party leader Malcolm Turnbull said that he was "disappointed" that Parry had not made the matter known "quite some time ago" to allow his election to be referred to the court simultaneously with the previous seven cases.

[204] On 6 November, Fairfax Media reported that Liberal MP John Alexander might hold British citizenship by descent, through his British-born father who migrated from the United Kingdom to Australia in 1911 at the age of three.

[77] Alexander immediately filed papers with the UK Home Office to renounce British citizenship[207] and on 17 November claimed that the application had been approved, making him eligible to stand in the by-election.

[204] However, Martin was the Mayor and Councillor of Devonport City Council, and the question of whether this disqualifies him from serving as a senator by reason of s 44(iv) of the Constitution (holding an office of profit under the Crown) was referred to the Full Court on 13 December 2017.

[99] On 1 February 2018, before any further court proceedings, Feeney announced his resignation from the House of Representatives, and confirmed that he had been unable to find documentation proving his renunciation of British citizenship.

Labor only narrowly won the suburban Melbourne electorate of Batman with Feeney in 2016, facing strong competition and losing the first-preference vote to the Greens' Alex Bhathal.

[231][232] A legal opinion by David Bennett QC, a former Commonwealth Solicitor-General, commissioned by the Liberal Party, is that Keay, along with Susan Lamb and Rebekha Sharkie, were ineligible under the High Court ruling because they were British citizens at nomination date.

Lamb claimed to have fulfilled all the requirements of section 44(i) as she believed she had taken all reasonable steps to renounce her citizenship – if it were the case that she was a British citizen – as she was unable to provide any further documents; she said she was estranged from her mother and that her father had passed away.

[citation needed] Labor MP Josh Wilson applied to renounce his British citizenship on 13 May 2016, the day after his unexpected endorsement as a candidate for the 2016 election, nominations for which closed on 9 June.

[citation needed] On 2 November 2017, questions were raised by The Australian concerning the possibility that Liberal MP and Minister Josh Frydenberg could be a citizen of Hungary under a Hungarian law designed to prevent statelessness caused during World War II.

[262] Prior to the implementation of the parliamentary Citizenship Register, several other MPs and Senators who were born outside Australia or are known to have at least one foreign-born parent have made statements clarifying that they were not dual citizens at the time of nominating as a candidate.