English military rule:
It was necessary to develop a basic legal system when Australia was colonised, especially since the population was (initially) largely composed of petty criminals given no other incentive to obey their social superiors. The Letters Patent of 1787 gave the Governor the power to establish a court of civil jurisdiction, while the New South Wales Act 1787 established a criminal court for that territory (it bears note that the whole of Australia was often referred to by this name - ‘Australia’ was a much later development). The criminal court consisted of military officers and a Judge-Advocate. The justice delivered was rather questionable, given the utter lack of legal expertise, convoluted legal roles and emphasis on expedience - the first years for the colonists were pretty grim and the only significant difference between convict and guard was the uniform. Nobody who was forcibly sent to Australia was sorely missed by Britain.
Modified English civil law:
Modifications were made to laws derived from England to meet the unique needs of the colony until an effective court and parliamentary system could be established. Penal (military) law became inappropriate when free settlers began arriving en masse and convicts were emancipated (as most deportees were given relatively light sentences in terms of imprisonment/forced labour duration, but exile to Australia might as well have been life).
Full reception of English law:
The Doctrine of Reception indicated that all English colonists carried with them the English law necessary to administer a colony governed by English rule. The doctrine distinguished between colonies occupied by conquest or cession and those claimed by ‘discovery’ and which were uncultivated. If the land was ‘found’, so the logic went, then English law immediately applied, without restriction. Differing cultural perspectives on land ownership led to conflict with the indigenous inhabitants and the concept of Terra Nullius came into vogue. Skirmishes, the establishment of frontiers saw many settlers and many more Aboriginal people killed - indeed, until the 1920s, hunting of indigenous peoples was officially sanctioned by the government.
The establishment of the Commonwealth:
The Federal system of law-making arose in Australia due to the colonies’ wishes to merge for reasons economic (the previous import/export taxation system was absurd), defensive (small population, geographical isolation) and social (common custom and culture) reasons. The move toward federation began properly in the 1890s when the notion was discussed at a series of constitutional conventions. As a response to the colonies’ fear of gradually losing power, the Senate was created in order to ensure that the newly-recognised states would retain most of their power upon transition and that all would possess equal voting rights. This latter point is debateable, as the passing of a referendum still requires a majority of voters in a majority of states - hence, the voters of populous New South Wales are disadvantaged. Nonetheless, the system was broadly accepted.
The development of a legally independent nation:
Having closely scrutinised the federal constitutions of the United States of America, Canada and Switzerland, the structure of the new state was set down with the composition of the Federal Parliament and the powers of its subordinate states as key considerations. The debate over state powers exists today and is referred to as the Division of Powers.
Preliminary high school curriculum notes, expanded and formatted. Thanks to Plasma for alerting me to my error about the so-called Separation of Powers.