Australia was uninhabited before stone-culture peoples arrived, perhaps by boat across the waters separating the island from the Indonesia archipelago about 40,000 years ago. Portuguese, Spanish, Dutch, and English explorers observed the island before 1770, when Captain Cook explored the east coast and claimed it for Great Britain (three American colonists were crew members aboard Cook's ship, the Endeavor).

On January 26, 1788 (now celebrated as Australia Day), the First Fleet under Capt. Arthur Phillip landed at Sydney, and formal proclamation of the establishment of the Colony of New South Wales followed on February 7. Many but by no means all of the first settlers were convicts, condemned for offenses that today would often be thought trivial. The mid-19th century saw the beginning of government policies to emancipate convicts and assist the immigration of free persons. The discovery of gold in 1851 led to increased population, wealth, and trade.

The six colonies that now constitute the states of the Australian Commonwealth were established in the following order: New South Wales, 1788; Tasmania, 1825; Western Australia, 1830; South Australia, 1836; Victoria, 1851; and Queensland, 1859.

Settlement had preceded these dates in most cases. Discussions between Australian and British representatives led to adoption by the British Government of an act to constitute the Commonwealth of Australia in 1900.

The first federal Parliament was opened at Melbourne in May 1901 by the Duke of York (later King George V). In May 1927, the seat of government was transferred to Canberra, a planned city designed by an American, Walter Burley Griffin. The first session of Parliament in that city was opened by another Duke of York (later King George VI). Australia passed the Statute of Westminster Adoption Act on October 9, 1942, which officially established Australia's complete autonomy in both internal and external affairs. Its passage formalized a situation that had existed for years. The Australia Act (1986) eliminated the last vestiges of British legal authority.