In terms of determining whether someone is a dual citizen, the High Court doesn’t just consider the issue according to the laws of the other potential country of citizenship.
In Sykes v Cleary, the majority found that, while issues of citizenship should first be considered according to the laws of the country of that citizenship, there are some qualifications:
But, there is no reason why s.44(i) should be read as if it were intended to give unqualified effect to that rule of international law. To do so might well result in the disqualification of Australian citizens on whom there was imposed involuntarily by operation of foreign law a continuing foreign nationality, notwithstanding that they had taken reasonable steps to renounce that foreign nationality. It would be wrong to interpret the constitutional provision in such a way as to disbar an Australian citizen who had taken all reasonable steps to divest himself or herself of any conflicting allegiance....
What is more, s.44(i) finds its place in a Constitution which was enacted at a time, like the present, when a high proportion of Australians, though born overseas, had adopted this country as their home. In that setting, it could scarcely have been intended to disqualify an Australian citizen for election to Parliament on account of his or her continuing to possess a foreign nationality, notwithstanding that he or she had taken reasonable steps to renounce that nationality.
In terms of what are “reasonable steps” for the purpose of s 44(i):
What amounts to the taking of reasonable steps to renounce foreign nationality must depend upon the circumstances of the particular case. What is reasonable will turn on the situation of the individual, the requirements of the foreign law and the extent of the connection between the individual and the foreign State of which he or she is alleged to be a subject or citizen. And it is relevant to bear in mind that a person who has participated in an Australian naturalization ceremony in which he or she has expressly renounced his or her foreign allegiance may well believe that, by becoming an Australian citizen, he or she has effectively renounced any foreign nationality.
Apparently, failing to make a demand to renounce former citizenship can mean that reasonably steps haven’t been taken. This was the case for the two candidates considered in Sykes v Cleary, who assumed that having been naturalised as Australian was enough to renounce their previous citizenship and then failed to take any other actions before standing for parliament.
Justice Brennan expanded a bit on the sorts of circumstances where someone might be considered a citizen of another country but would not be disqualified for the purpose of s 44(i):
One such situation does occur when the foreign law, purporting to affect nationality of persons who have had no connection or only a very slender connection with the foreign power, exceeds the jurisdiction recognized by international law. That is the situation described by Lord Cross ((58) supra, fn.(53)) in which international law does not recognize the jurisdiction of the foreign power. A second situation occurs when an Australian citizen has done all that lies reasonably within his or her power (i) to renounce the status or the rights or privileges conferred by the foreign law carrying a reciprocal duty of allegiance or obedience to the foreign power and (ii) to obtain a release from any such duty. It is not sufficient, in the second situation, for a person holding dual citizenship to make a unilateral declaration renouncing foreign citizenship when some further step can reasonably be taken which will be effective under the relevant foreign law to release that person from the duty of allegiance or obedience. So long as that duty remains under the foreign law, its enforcement - perhaps extending to foreign military service - is a threatened impediment to the giving of unqualified allegiance to Australia. It is only after all reasonable steps have been taken under the relevant foreign law to renounce the status, rights and privileges carrying the duty of allegiance or obedience and to obtain a release from that duty that it is possible to say that the purpose of s.44(i) would not be fulfilled by recognition of the foreign law.
So, again, he refers to this question of “reasonable steps”.
Justice Deane clarifies that the law doesn’t apply to Australian born people who might be eligible for foreign citizenship, but who haven’t really consented to gaining that foreign citizenship:
In conformity with the purpose of the sub-section, the second limb (i.e. "is a subject or a citizen or entitled to the rights or privileges of a subject or citizen of a foreign power") should, in my view, be construed as impliedly containing a similar mental element with the result that it applies only to cases where the relevant status, rights or privileges have been sought, accepted, asserted or acquiesced in by the person concerned. The effect of that construction of the sub-section is that an Australian-born citizen is not disqualified by reason of the second limb of s.44(i) unless he or she has established, asserted, accepted, or acquiesced in, the relevant relationship with the foreign power.
And for foreign born people, he again talks about the issue of “reasonable steps”:
A person who becomes an Australian citizen will not be within the second limb of s.44(i) if he or she has done all that can reasonably be expected of him or her to extinguish any former relationship with a foreign country to the extent that it involves the status, rights or privileges referred to in the sub-section.
Justice Deane comes to a different decision to some of the other justices about how the law should be applied, though, so you can’t automatically take his quotes as definitive statements of the law.
So, basically, the question seems to go (speaking very generally):
Is the candidate regarded by another country as a citizen;
Was the candidate born overseas and therefore entitled to other citizenship, or otherwise done anything to seek, accept, assert or acquiesce in citizenship of another country?
Has the candidate taken reasonable steps to renounce their other citizenship and to obtain a release from any duties associated with that other citizenship?
Anyway, that’s my best interpretation of it.
