It's complicated.
The Australian constitution says:
44. Any person who—
(i) Is under any acknowledgment of allegiance, obedience, or adherence to a foreign power, or is a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power: or
...(snipped other disqualifications)...
shall be incapable of being chosen or of sitting as a senator or a member of the House of Representatives
As the Prime Minister is a member of the House of Representatives, this prohibition applies to the PM. However, our PM is not our head of state; The Queen of England is, and as such, our head of state is ALWAYS going to be a foreigner.
To further complicate matters, in 1900, when the Constitution was written, Australia was a part of the British Empire, and 'foreign power' implied foreign to the empire, rather than foreign to the nation state - a British Subject was not considered a 'citizen of a foreign power' at that time. This has led to considerable debate regarding the eligibility of candidates under Section 44(i), particularly as many countries do not allow the renunciation of citizenship. As many Australian Senators, Representatives, and even Prime Ministers have been born outside Australia, the question has been considered a number of times by the High Court.
In
Sykes v Cleary (25 November 1992), all seven judges of the High Court found that s.44(i) required a person to take 'all reasonable steps' to renounce their other citizenship. The majority of the court (five of seven judges) held that this required use of the renunciation procedures of the other country if there were such procedures; Where there were no such procedures, or where the other country refused renunciation, proof of requesting renunciation was sufficient.
So in the case of an Australian Citizen born in the UK, it is lawful to run for parliament only if one can produce proof of requesting renunciation of ones British citizenship; Typically this would consist of UK Visa and Immigration Form RN, officially signed and stamped by the Home Office.
No such proof has been made public (despite repeated requests from a variety of sources, including MPs, including requests under the Freedom of Information Act) for former PM Tony Abbott, who was born in London, England; As such, it is quite possible that his entire tenure as MP for Warringah, and as PM, were unlawful.
To resolve the confusion, the Australian Electoral Commission recommended in a 2010 report (amongst other recommendations) that a future constitutional amendment should:
- delete subsection 44(i).
- insert a new provision requiring candidates and members of parliament to be Australian citizens.
- empower parliament to enact legislation determining the grounds for disqualification of members of parliament in relation to foreign allegiance.
However as such an amendment would require a referendum, it is unlikely that this recommendation will come to pass, unless the change is included in a wider referendum on constitutional reform; Such referenda require the support of both a majority of voters, and a majority of states, in order to become law.
