John Cain (26 April 1931 – 23 December 2019) was an Australian politician who was the 41st Premier of Victoria, in office from 1982 to 1990 as leader of the Labor Party. During his time as premier, reforms were introduced such as liberalised shop trading hours and liquor laws, equal opportunity initiatives, and occupational health and safety legislation.

Cain was born in Northcote, Victoria, where his father, John Cain, the leader of the Australian Labor Party in Victoria from 1937 to 1957 and three times premier, was the local member. His mother ran a successful chain of millinery stores in the inner north of Melbourne.

He was educated at Bell Primary School, Northcote High School, Scotch College, and at the University of Melbourne, where he graduated in law in 1952. He practised law in suburban Melbourne, and was president of the Law Institute of Victoria in 1972–73. He was also a member of the Law Council of Australia and a member of the Australian Law Reform Commission.

Cain was 24 when the 1955 split in the Labor Party brought down his father's last government. He lost a preselection battle with Frank Wilkes for his father's seat of Northcote after his father died in 1957.

During the 1960s, he was a member of the group, known as The Participants, which also included John Button, Richard McGarvie, Frank Costigan and Barry Jones, who opposed the left-wing group which controlled the Victorian Labor Party from 1955 onwards. In 1971 he supported moves by supporters of Gough Whitlam, led by Bob Hawke and others, that in 1971 brought about federal intervention in the Victorian branch and ended left-wing control. He became vice-chairman of the Victorian Labor Party in 1973. That group of Participants later became known as the Independents faction which predominantly voted with the Socialist Left.

In 1976, Cain was elected to the Victorian Legislative Assembly as MP for Bundoora. He became shadow Attorney-General under the leadership of Frank Wilkes. After Wilkes narrowly lost the 1979 election to the Liberal premier, Dick Hamer, Cain challenged him for the leadership, becoming leader in September 1981.

Hamer had been forced to resign a few months earlier and was succeeded by deputy premier Lindsay Thompson. However, the Liberals appeared tired and complacent after over a quarter-century in power, and Cain consistently got the better of Thompson. After waiting as long as he could, Thompson called an election for April 1982. At that election, Labor won a sweeping victory on a 17-seat swing—the worst defeat that a non-Labor government has ever suffered in Victoria. Cain took office at the helm of the first Labor government in Victoria since the one led by his father 27 years earlier.

During its first term, Cain's government carried out many reforms, particularly in the areas of education, environment, law reform and public administration. The Government brought in nude beaches, legalised many brothels, extended Saturday shop trading hours, extended nightclub hours, extended hotel hours, permitted football matches to take place on Sundays, and furnished more gambling opportunities.