Alfred Deakin (3 August 1856 – 7 October 1919) was an Australian politician who served as the second Prime Minister of Australia. He was a leader of the movement for Federation, which occurred in 1901. During his three terms as prime minister over the subsequent decade (1903–1904, 1905–1908, 1909–1910), he played a key role in establishing national institutions.

Deakin was born in Melbourne to middle-class parents. He was elected to the Victorian Legislative Assembly in 1879, aged 23, additionally working as a barrister and journalist. He held ministerial office sporadically beginning in 1883, serving twice as Attorney-General of Victoria and aligning himself with liberal and radical reformers. In the 1890s Deakin became one of the leading figures in the movement for the federation of the Australian colonies. He was a delegate to the federal conventions and served on the committees that drafted the federal constitution. He later campaigned at a series of referendums and lobbied the British government for its adoption.

After Federation in 1901, Deakin became the inaugural Attorney-General of Australia in the ministry led by his close friend Edmund Barton. He succeeded Barton as prime minister in September 1903. Two subsequent elections in 1903 and 1906 produced an even split between three parties, with Deakin’s Liberal Protectionists occupying an effective middle ground between the Free Traders and the Australian Labor Party (ALP). He left office in April 1904 following an unproductive first term, but returned in July 1905 and was able to form a functional government with the support of the ALP. He relinquished office again in August 1908.

In 1909, in what became known as the Fusion, Deakin controversially led his supporters into a union with the Free Traders. Their alliance, based on anti-socialism, marked the beginning of a two-party system in federal politics and allowed him to form Australia’s first majority government. Deakin regarded his final term as prime minister, from June 1909 to April 1910, as his most productive. However, to his surprise the ALP won a majority in both houses at the 1910 election. He retired from politics in 1913, in the early stages of a degenerative neurological condition that led to his death at the age of 63.

Deakin is regarded as one of Australia's most influential prime ministers. He was the principal architect of the "Australian settlement", the features of which – the White Australia policy, compulsory arbitration, protectionism, state paternalism, and support for the British Empire – formed the basis of Australia's socio-economic framework well into the 20th century.