Australia's dual citizenship saga continues to claim victims, with the High Court on May 9 finding former senator Katy Gallagher – a British-Australian dual citizen at the time nominations closed for the 2016 election - ineligible to sit in parliament.

The finding prompted the resignations of four MPs in similar positions.

An electoral law expert, Professor Graeme Orr, of the University of Queensland, put the law in context on ABC News Breakfast the following day:

"It's more than ironic that the High Court can have people on it who are dual citizens [who] make and shape the fundamental law of the land, but it's not good enough for the Australian Parliament...These laws do not apply at state level. Why they have to apply at Commonwealth level I do not know. "

Can you be a dual citizen and sit on the High Court? RMIT ABC Fact Check finds out.

The verdict

Professor Orr's claim checks out.

The Australian Constitution does not prevent dual citizens from sitting as High Court judges.

Former Labor senator Katy Gallagher argued she took all reasonable steps to renounce her British citizenship. The High Court disagreed. ( AAP Image/Lukas Coch )

Under the constitution, justices of the High Court are appointed by the governor-general in council, effectively the government of the day.

The sole constitutional restriction is that a justice has to retire when they turn 70, and cannot be appointed if they are 70 or over.

A Commonwealth law – the High Court Act 1979 – adds that to be eligible for appointment, a justice has to have been a judge of a Commonwealth, state or territory court (other than the Local Court of the Northern Territory) or an Australian barrister or solicitor for at least five years.

The prohibition on dual citizenship for federal politicians could be seen as a unique aspect of the Australian system. Dual citizens are able to sit in state and territory parliaments, subject to some exceptions for people who obtain foreign citizenship while in parliament.

What is the claim about?

During his appearance on News Breakfast, Professor Orr argued that section 44 was unnecessary and should be put to a referendum.

He told Fact Check:

"It was a rhetorical point and not meant to impugn the High Court – far from it – but to show our blindness to the illogic of barring 'dual citizens' from being MPs. A single MP out of 226 MPs voting on party lines has less power to shape the law than one of the seven on the High Court. There's no clear rationale why we would block an Australian citizen from high office – let alone block fellow electors for voting for them – simply because they inherited another citizenship."

Who can be a High Court Judge?

The High Court currently consists of seven members. There have been 13 chief justices and 42 justices since the court was established in 1903.

Professor John Williams, of the University of Adelaide Law School, told Fact Check: "There is nothing in the constitution that says anything about the qualification of members of the High Court."

Section 72 of the Constitution sets out the conditions of "Judges' appointment, tenure and remuneration".

The Justices of the High Court and of the other courts created by the Parliament: 1. shall be appointed by the Governor-General in Council; 2. shall not be removed except by the Governor-General in Council, on an address from both Houses of the Parliament in the same session, praying for such removal on the ground of proved misbehaviour or incapacity; 3. shall receive such remuneration as the Parliament may fix; but the remuneration shall not be diminished during their continuance in office. The appointment of a Justice of the High Court shall be for a term expiring upon his attaining the age of seventy years, and a person shall not be appointed as a Justice of the High Court if he has attained that age.

Section 7 of the High Court Act 1979 sets out some qualifications based on experience:

A person shall not be appointed as a Justice unless: (a) he or she is or has been a Judge of a court created by the Parliament or of a court of a State or Territory (other than a Judge or acting Judge of the Local Court of the Northern Territory); or (b) he or she has been enrolled as a barrister or solicitor, as a barrister and solicitor, or as a legal practitioner, of the High Court or of the Supreme Court of a State or Territory for not less than 5 years.

Professor Kim Rubenstein, of the Australian National University Law School, said that apart from the age and experience criteria, appointment of High Court justices "is entirely in the discretion of the governor-general in council".

It is unclear if any current justices are dual citizens, although some prominent former judges were born overseas, including former justice Dyson Hayden, who was born in Canada and served on the court between 2003 and 2013, and the late Sir Ninian Stephen, who was born in the UK and served between 1972 and 1982. Sir Ninian left the court to become governor-general (1982 to 1989).

And the states?

It is only candidates at the federal level who are required by the constitution to renounce any foreign citizenship before seeking election.

Dual citizens are eligible to stand for election to state and territory parliaments, subject in some cases to restrictions on people who attain foreign citizenship after their election.

In a recent article, Professor Orr wrote:

"The oddity of a modern, let alone immigrant, nation rationing fundamental political rights to sole citizens is blatantly apparent. None of the Australian States or Territories retains such a chauvinist rule. Most States merely require a serving MP to forfeit their seat if they take out a foreign citizenship or allegiance; Victoria does not even bother with that largely symbolic rule."

For instance, under section 17 of the South Australian Constitution Act 1934, a member of the Legislative Council (the state's upper house) would lose their seat if:

they are not – or they stop being – an Australian citizen;

they are not – or they stop being – an Australian citizen; "takes any oath or makes any declaration or act of acknowledgment or allegiance to any foreign prince or power"; or,

"takes any oath or makes any declaration or act of acknowledgment or allegiance to any foreign prince or power"; or, "does, concurs in, or adopts any act whereby the member may become a subject or citizen of any foreign state or power."

However, it is also notes: "The seat of a member of the Legislative Council is not vacated because the member acquires or uses a foreign passport or travel document."

Professor Williams told Fact Check that "in South Australia, they changed the state constitution after Sykes v Cleary", the now well-known 1992 decision on section 44 of the Commonwealth constitution.

As noted in Fact Check's earlier Fact File on Dual Citizenship, the majority of the court in Sykes v Cleary (five out of the seven judges, with justices William Deane and Mary Gaudron dissenting) found that a citizen who is a subject or citizen of a foreign state had to take all reasonable steps under the foreign state's laws to renounce that nationality, before being eligible to stand for election in Australia.

Principal researcher: Paul Crossley

Sources