In 1788 during his first voyage to the Pacific, Royal Navy captain James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain.[1] Seventeen years later, following the loss of its American colonies in 1783, the British Government sent a fleet of ships, the "First Fleet", under the command of Captain Arthur Phillip, to establish a new penal colony in New South Wales. A camp was set up and the flag raised at Sydney Cove on 26 January 1788, and the British Crown Colony of New South Wales was formally promulgated on 7 February 1788. Further Crown Colonies were established in Van Diemen's Land (now known as Tasmania) in 1803; Swan River Colony (now known as Western Australia) in 1828; South Australia in 1836; Victoria in 1851; and Queensland in 1859. The six colonies federated in 1901 and the Commonwealth of Australia was formed as a Dominion of the British Empire.

Australia fought alongside Britain and its Allies in World War I, notably at Gallipoli (against the Ottoman Empire) and the Western Front. It fought with Britain and its allies again in World War II, protecting Britain's Pacific colonies from Imperial Japan.

Until 1949, Britain and Australia shared a common nationality code. The final constitutional ties between the United Kingdom and Australia ended in 1986 with the passing of the Australia Act 1986.

Formal economic relations between the two countries declined following Britain's accession to the European Economic Community in 1973. Nevertheless, the United Kingdom remains the second largest overall foreign investor in Australia. In turn, Australia is the seventh largest foreign direct investor in Britain.

Due to Australia's history as a colony of Britain, the two nations retain significant shared threads of cultural heritage, many of which are common to all English-speaking countries. English is the de facto language of both nations. Both legal systems are based on the common law.

Pom is a common nickname given by Australians to British people, said in jest without malice or prejudice, in a similar way to how British (and other) people call Australians Aussies, and refer to Australia as "Oz" or "down under" (a reference to the fact that Australia is notable for being entirely in the southern hemisphere).