Sir William John Lyne KCMG (6 April 1844 – 3 August 1913) was an Australian politician who served as Premier of New South Wales from 1899 to 1901, and later as a federal cabinet minister under Edmund Barton and Alfred Deakin.

He is best known as the subject of the so called "Hopetoun Blunder", unexpectedly being asked to serve as the first Prime Minister of Australia but proving unable to form a government.

Hopetoun was relying on the precedent established at Canadian Confederation, where the premier of the largest colony became the prime minister of the new federation.

Lyne opposed the formation of the new Commonwealth Liberal Party in 1909 and spent the rest of his career as a crossbencher, supporting Andrew Fisher's Labor government.

[5] George Reid won the 1895 election on behalf of free traders, and Lyne became Leader of the Opposition as Dibbs had lost his seat.

But within twelve months the fracturing of George Reid's free trade government by the issue of Federation made possible a protectionist minority government as long as Lyne replaced Barton, and accordingly Lyne resumed leadership of protectionists in August 1899.

[3][6] Lyne promised the Labor Party specific reforms and he passed 85 Acts between July and December 1900, including early closing of retail shops, coal mines regulation and miners' accident relief, old-age pensions and graduated death duties.

He was one of the representatives of New South Wales at the 1897-8 convention, and sat on its finance committee, but was absent from 49 percent of its divisions, the worst record of any delegate but one.

The Governor-General, Lord Hopetoun, was also of this mind, and offered the post to Lyne in December 1900, heading an interim government that would serve until the first federal election.

Eventually, Hopetoun was forced to accept the majority view that Edmund Barton, the leader of the federation movement, should be prime minister.

Lyne became Minister for Home Affairs in Barton's cabinet on 1 January 1901 and was elected to the first federal Parliament as member for the Division of Hume in March 1901.

The general election held in December 1903 resulted in the return of three nearly equal parties, and Deakin was forced to resign in April 1904 but came back into power in July 1905 with Lyne in his old position.

In April 1907 Lyne accompanied Deakin to the colonial conference and endeavoured to persuade the British politicians that they were foolish in clinging to their policy of free trade.

[3] Lyne's name is associated with the 'Lyne Tariff'— the Customs Tariff Act of 1908—which significantly increased levels of protection for local industry.

[9] It represented the final triumph of politicians favouring protection, over those advocating free trade, and brought to an end the main political divergence of pre-Federation Australia.

In his early political life he was a great advocate of irrigation, and in federal politics he had much to do with the shaping of the policy of protection eventually adopted by the Commonwealth.His reputation has been sullied by Alfred Deakin's description of him as "a crude, sleek, suspicious, blundering, short-sighted, backblocks politician".

[12] Lyne was also largely responsible for pushing through Parliament the bounty scheme that brought the Thylacine (Tasmanian tiger) to its extinction.