The Constitutional history of Australia is the history of Australia's foundational legal principles. Australia's legal origins as a nation state began in the colonial era, with the reception of English law and the lack of any regard to existing Indigenous legal structures. As the colonies expanded, Australia gradually began to achieve de facto independence. Over the years as a result the foundations of the Australian legal system gradually began to shift. This culminated in the Australia Act, an act formally ending legal ties with the UK.

Settlement Prior to European settlement of Australia, Europeans had been to the land merely as explorers. The only exception was James Cook who in 1770 sailed up most of the east coast of Australia and then claimed the entire coastline he had just explored as British territory. No formal legal justification was made of the claim at the time, but in any event no regard was given to any potential Indigenous legal rights.

Orders-in-Council were issued in London on 6 December 1785 for the establishment of a colony in Botany Bay. Arthur Phillip was appointed Governor-designate of the new colony in October 1786. In Phillip's commission, the boundary was defined as the 135th meridian east longitude (135° east), (26 January 1788 – Map) taking the line from Melchisédech Thévenot's chart, Hollandia Nova‒‒Terre Australe, published in Relations de Divers Voyages Curieux (Paris, 1663).Sir Joseph Banks, 'Draft of proposed Introduction to Captn Flinders Voyages', November 1811; State Library of New South Wales, The Papers of Sir Joseph Banks, Series 70.16; quoted in Robert J. King, "Terra Australis, New Holland and New South Wales: the Treaty of Tordesillas and Australia", The Globe, no.47, 1998, pp. 35–55, p. 35.

Soon after Lord Sydney appointed him governor, Phillip drew up a detailed memorandum of his plans for the proposed new colony. In one paragraph he wrote: "The laws of this country [England] will of course, be introduced in [New] South Wales, and there is one that I would wish to take place from the moment his Majesty's forces take possession of the country: That there can be no slavery in a free land, and consequently no slaves." European settlement commenced with the arrival of the First Fleet, comprising 11 ships which arrived at Botany Bay, New South Wales between 18 and 20 January 1788. The Fleet brought a total of 1044 people to the new settlement, of whom 696 were convicts. The actual settlement was located at Sydney Cove. The colony was formally proclaimed by Governor Phillip on 7 February 1788 at Sydney. Though the settlement was a military prison, and Phillip had full power as governor, the colony also had a civil administration and courts of law.

The application of English law to the Indigenous population remained unsettled however. In R v TommyR v Tommy (Supreme Court of New South Wales, Forbes CJ, 24 November 1827) via Austlii an Aboriginal man was found liable under law for the murder of a colonist. Later, in the case of R v Ballard the court held it did not have the jurisdiction to convict an Aboriginal man of murdering another Aboriginal man as English law did not apply to them. However, this judgment was implicitly overturned in the case of R v Murrel, where the court held that Aboriginal people had no law and could be convicted for the murder of each other.

In 1835, Governor Bourke proclaimed that Indigenous Australians could not sell or assign land, nor could an individual person or group acquire land, other than through distribution by the Crown. The proclamation was approved by the Colonial Office on 10 October 1835. The proclamation was issued in response to the attempt by graziers from Van Diemen's Land to enter into an agreement with indigenous tribes in Port Philip, known as Batman's Treaty.

During the 19th century, separate British colonies were formed in Australia. In 1825, Tasmania, named Van Diemen's Land, was proclaimed a separate colony from the colony of New South Wales. The Swan River Colony of Western Australia was established in 1832, separately from that of New South Wales, effectively taking over by Britain of the remainder of the Australian continent. Following the Treaty of Waitangi, William Hobson declared British sovereignty over New Zealand in 1840 and was part of the colony of New South Wales. In 1841, it was separated from the colony of New South Wales to form the new Colony of New Zealand.By letters patent, the British government issued the Charter for Erecting the Colony of New Zealand on 16 November 1840. South Australia was formed in 1836 separately of the colony of New South Wales, and Victoria in 1851 and Queensland in 1859 both from the colony of New South Wales. By Letters Patent on 6 June 1859, Queen Victoria gave her approval to the separation of the colony of Queensland from New South Wales. On the same day an Order-in-Council gave Queensland its own Constitution. Queensland became a self-governing colony with its own Governor, a nominated Legislative Council and an elected Legislative Assembly. South Australia was founded as a "free province"—it was never a penal colony. Victoria and Western Australia were also founded "free", but later accepted transported convicts. A campaign by the settlers of New South Wales led to the end of convict transportation to that colony; the last convict ship arrived in 1848.

Responsible government

Between 1855 and 1890, the six colonies individually gained responsible government, managing most of their own affairs while remaining part of the British Empire. The Colonial Office in London retained control of some matters, notably foreign affairs, defence, and international shipping. New Zealand achieved responsible government in 1853, New South Wales and Victoria in 1855, Tasmania in 1856, Queensland in 1859 (separated from New South Wales in that year with self-government from the beginning) and Western Australia in 1890. These arrangements were confirmed by the Colonial Laws Validity Act 1865.

The Colonial Laws Validity Act 1865 was a British Act of Parliament to define the relationship between local ("colonial") and British ("imperial") legislation. It confirmed that colonial legislation was to have full effect within the colony, limited only to the extent that it was not in contradiction with ("repugnant to") any Imperial Act which extended to that colony. The Act had the effect of clarifying and strengthening the position of colonial legislatures, while at the same time restating their ultimate subordination to the British Parliament.

Until the passage of the Act, a number of colonial statutes had been struck down by local judges on the grounds of repugnancy to English laws (whether or not those English laws had been intended by Parliament to be effective in the colony). This had been a particular problem for the government in South Australia, where Justice Benjamin Boothby had struck down local statutes on numerous occasions in the colony's Supreme Court.see for example Dawes v Quarrel (1865) Pelham's Reports 1 at p. 8 Supreme Court of SA (18 July 1865).

Towards federation The first formal steps to federation of the colonies was in the form of the Federal Council of Australasia in 1885. However, the council was a weak non-executive, non-legislative federation of Western Australia, Fiji, Queensland, Tasmania and Victoria. The movement for full federation developed in the late 19th century, culminating in the six Australian colonies forming a federation of States. It was envisaged that New Zealand might also join.

In the 1890s, two constitutional conventions were called, which ultimately adopted a constitution based on a combination of British, American and other models (monarchy and parliamentary government from Britain, federalism from Canada and the United States, the use of the referendum from Switzerland). This constitution was then approved by the voters in each of the six colonies. (At the time women had the vote in only one of them: South Australia, and Aboriginal Australians in South Australia and Queensland only).

It was then passed (with an amendment allowing for some appeals to the Privy Council in London) as an Act of the British Parliament: the Commonwealth of Australia Constitution Act 1900. The Act entered into force on 1 January 1901, at which point the Commonwealth of Australia came into being.

The Australian Constitution, besides other matters, dealt with the allocation of powers between the colonies, which became states, and the federal parliament. Most of the powers, including those of foreign affairs and defence, were concurrent powers, with the proviso that if there was a conflict between the federal and a state law, then the federal law "will prevail". But the United Kingdom still had the power to engage in foreign affairs on behalf of Australia, and to make laws for it. In the early years Australia continued to be represented by the United Kingdom as part of the British Empire at international conferences. In 1919, following Canadian lead, Australian Prime Minister Billy Hughes insisted that Australia have separate representatives at the Versailles Peace Conference and not as part of the British delegation.

The Constitution provided that the British monarch be represented in Australia by a Governor-General. Originally, appointments were made on the advice of the British, not the Australian, government, and was generally a British aristocrat. In 1930, the Australian government insisted that Australian-born Isaac Isaacs be appointed. The British government very reluctantly accepted the Australian position that such appointments be made on the advice of the Australian government.

Finally, the Constitution provided that any law of the Australian Parliament could be disallowed within a year by the British monarch (acting on the advice of British ministers), though this power was never in fact exercised. In summary, the constitutional position of the Commonwealth as a whole in relation to the United Kingdom was, originally, the same as that of the individual colonies before federation.

From a united imperial Crown to a shared monarch A fundamental change in the constitutional structures of the British Commonwealth (formerly the British Empire, and not to be confused with the Commonwealth of Australia) did occur, however, in the late 1920s. Under the British Royal and Parliamentary Titles Act 1927, which implemented a decision of an earlier Commonwealth conference, the unified Crown that had heretofore been the centre point of the Empire was replaced by multiple crowns worn by a shared monarch.

Before 1927, King George V reigned as king in Australia, New Zealand, Canada, the Irish Free State, South Africa, etc., each of these states, in effect, as dominions, amounting to a subset of the United Kingdom. After 1927, he reigned as King of Australia, New Zealand, Canada, Ireland, South Africa, etc.

The form of use in the royal title as issued by King George V did not mention the dominions by name, except 'Ireland', which changed from being referred to as Great Britain and Ireland to Great Britain, Ireland, indicating that it was no longer part of the United Kingdom, but a separate state of which the monarch was now directly the head, rather than through linkage with Great Britain. Though unnamed, except through reference to the 'British Dominions beyond the Seas', the ground-breaking move shattered the previous concept of the shared monarch to one of multiple monarchies, all held by the one monarch.