The Governor is the Constitutional Head of the State, the High Court has declared unanimously, ending the debate which one eminent republican says is “arid” and “irrelevant.” This is a separate issue to the question whether the Governor-General is a Head of State under international law. There is only one answer to that question, a matter which is discussed in The Cane Toad Republic, 1999. For purposes of international diplomacy and international law, the Governor-General is, unequivocally, a Head of State. The High Court decision relates to constitutional, not international law. This was concerned an application by an elector for the Court to order a Governor to initiate action to fill a senate vacancy. The Court said:
“The Governor, as the officiating Constitutional Head of the State, is accordingly named as the person to whom the notification is to be given, and the notification must be regarded as addressed to him in that capacity. So, in certifying to the Governor General the names of the senators elected, chosen, or appointed the Governor must be regarded as acting in the capacity of the Constitutional Head of the State, being in that capacity the proper channel of communication with the officiating Constitutional Head of the Commonwealth, the Governor General.”
The High Court continued (the words in brackets have been added for the understanding of this edited extract):
“We think that he must be regarded as acting in the same capacity (ie a Constitutional Head of State) when discharging the function of issuing a writ for the election of senators under sec. 12 (of the Federal Constiution)…We will assume, without deciding, that sec. 12 imposes a duty upon the Governor to issue a writ in such a case. But the question remains: To whom does he owe this duty? … It has never been suggested that if the Governor failed to issue the writs (for a state election) a mandamus would lie from a State Court to compel him to do so. (that is, a State Supreme Court could order the Governor to issue the writs).
“There is, of course, a remedy in such a case but it is to be sought from the direct intervention of the Sovereign and not by recourse to a Court of law. The case of an election to the Senate is not quite analogous. It is conceivable that the Executive Government of a State for the time being might desire that no senator should be chosen to fill a particular vacancy. If they advised the Governor to abstain from taking any action to fill it, and… he accordingly did nothing, it may be that he would have failed in his duty… [I]t is clear that the duty would be one which he owed to the State collectively.
“It is not easy to see how, in such a case, he could perform this duty without dismissing his Ministers and finding others, and that power is manifestly one the exercise of which could not be reviewed by any authority but the Sovereign. The duty, therefore, is one of the duties which the Constitutional Head of a State owes to the State (and in the case of a Governor, but in a slightly different sense, to the Sovereign), and its performance must be enforced in the manner appropriate to the case of such duties. Instances of such duties—duties of imperfect obligation—are familiar to students of Constitutional Law.
“It follows…(that) …the Governor … cannot be regarded quoad hoc (to this extent) as an officer of the Commonwealth. The States are not subordinate to the Commonwealth, and the Commonwealth Judiciary cannot command the Constitutional Head of a State to do in that capacity an act which is primarily a State function.”
The position is quite clear then. The Governor is the Constitutional Head of the State, and the Governor-General is the Constitutional Head of the Commonwealth.
The High Court has said so, unanimously. This was in The King v The Governor of the State of South Australia  HCA 31 ; (1907) 4 CLR 1497. (Thanks to a longstanding project of the law schools of the University of Technology, Sydney and the University of New South Wales, you can read the full judgment on the internet. There is a link to the case on the ACM site, as there is to most references in these columns)
As you can see, this was handed down on 8 August 1907. The chief Justice, Sir Samuel Griffith presided. Among the concurring judges was the future first Australian Governor-General Sir Isaac Isaacs, who was less inclined to support state rights than the other judges. Sir John Downer K.C., of that prominent family, appeared for “the prosecutor”, ie. the person seeking the order.