The Constitution is the legal framework for how Australia is governed. It was drafted at a series of conventions held in the 1890s by elected representatives from each of the colonies.

The final draft of the Constitution was approved by a vote of the people in referenda held in each colony between June 1899 and July 1900. An Australian delegation travelled to London to present the Constitution, which was part of the Commonwealth of Australia Constitution Bill, to the British Parliament. It was passed by the British Parliament as part of the Commonwealth of Australia Constitution Act 1900 and approved by Queen Victoria on 9 July 1900 when she signed the Royal Commission of Assent.

The Act, which took effect on 1 January 1901, stated that the colonies of New South Wales, Victoria, South Australia, Queensland and Tasmania would be united and known as the Commonwealth of Australia. The Constitution Act also made provision for Western Australia to join the Commonwealth. Western Australia agreed to federate in a referendum held on 31 July 1900, two weeks after the Act was passed.