Sir John Robert Kerr (24 September 1914 – 24 March 1991) was an Australian barrister and judge who served as the 18th governor-general of Australia, in office from 1974 to 1977. He is primarily known for his involvement in the 1975 constitutional crisis, which culminated in the controversial decision to dismiss the incumbent prime minister Gough Whitlam and appoint Malcolm Fraser as his replacement.

Kerr was born in Sydney to working-class parents. He won scholarships to Fort Street Boys' High School and the University of Sydney, where he studied law. His legal career was interrupted by the Second World War, during which he served with the Australian Army's Directorate of Research and Civil Affairs (DORCA) and attained the rank of colonel. After the war's end he became the inaugural head of the Australian School of Pacific Administration. Kerr returned to the bar in 1949 and became one of Sydney's leading industrial lawyers. He joined the Australian Labor Party (ALP) and was briefly an endorsed candidate for the 1951 federal election. He let his membership lapse after the party split of 1955.

Kerr served terms as president of the New South Wales Bar Association and the Law Council of Australia. He was appointed to the Commonwealth Industrial Court in 1966, later serving on territory supreme courts and as Chief Justice of New South Wales (1972–1974). On the nomination of ALP prime minister Gough Whitlam, Kerr was appointed governor-general in July 1974. The Whitlam government did not hold a majority in the Senate, and following a series of controversies in 1975, most notably the Loans Affair, the Liberal opposition leader Malcolm Fraser called on the Senate (where his coalition had a majority) to defer consideration of the supply bills in an attempt to force an early election. Kerr regarded the situation as untenable, believing the prime minister was obliged to either resign or call a general election, which Whitlam was unwilling to do.

On 11 November 1975, Kerr used his reserve powers as governor-general to dismiss Whitlam and his ministry, appointing Fraser to lead a caretaker government. He immediately granted Fraser's request for a double dissolution, leading to a federal election that saw Whitlam and the ALP defeated in a landslide. The dismissal of the government sparked demonstrations from Whitlam's supporters, with the anger directed at Kerr a major factor in his early retirement in December 1977 and subsequent withdrawal from public life. The propriety, legality and wisdom of his actions surrounding the dismissal have been subject to considerable debate and analysis.

Kerr was born in Balmain, Sydney, on 24 September 1914. He was the eldest of three children born to Laura May (née Cardwell) and Harry Kerr; his younger brother Dudley was born in 1917 and younger sister Elaine in 1926. Kerr's parents and maternal grandparents were Australian-born, while his paternal grandparents came from Sunderland, England, arriving in Sydney in 1886. He came from a line of waterside workers—his father was a boilermaker, his grandfather was a stevedore, and his great-grandfather was a shipwright. At the time of his son's birth, Kerr's father was employed at the Eveleigh Railway Workshops. He was sacked three months later, but soon found work at the Cockatoo Island Dockyard, which were at full capacity due to the ongoing war. He was involved in the union movement, and participated in a number of strikes, including the 1917 general strike, during which he went without pay for two months. Work at the docks became irregular after the war's end, and he eventually rejoined the railways in 1925.

For the first two years of his life, Kerr and his parents lived with his paternal grandparents in a weatherboard cottage at 25 Short St, Balmain. They later rented cottages in Rozelle and Dulwich Hill, buying the latter outright only in 1949. Kerr began his education at the Birchgrove Public School. He won a scholarship to attend the prestigious Fort Street Boys' High School, where he excelled academically. He topped the school in English, history, and chemistry in his final year. His contemporaries remembered him as quite aloof; one of his few close friends was Francis James. In deciding to pursue law as a career, Kerr found a role model in H. V. Evatt, a fellow Fortian who in 1930 became the youngest-ever High Court judge; in the same year, Evatt completed a doctoral thesis on the royal prerogative. Kerr's father knew Evatt through his membership of the Labor Party, which Evatt would eventually lead, and had helped him on his successful campaign for the state seat of Balmain in 1925. Evatt became the first in a series of patrons who helped Kerr progress in his career despite a relatively humble background.

In 1932, Kerr began studying law at the University of Sydney. He again excelled academically, winning a number of prizes, but had little interest in extra-curricular activities. One of his closest friends was Ken Gee, who eventually joined him on the judiciary but was also known for his flirtation with Trotskyism. Kerr eventually graduated in 1936 with first-class honours and the University Medal. He was called to the New South Wales bar in 1938. The same year, Kerr married Alison "Peggy" Worstead, with whom he had three children. He spent World War II working for the Australian intelligence organisation and think tank, the Directorate of Research and Civil Affairs. In 1946 he became principal of the Australian School of Pacific Administration and the first Secretary-General of the South Pacific Commission.

Kerr returned to the bar in 1948, becoming a prominent lawyer representing trade union clients and a member of the Labor Party. In the early 1950s he represented Laurie Short in his successful attempts to unseat the leadership of the Federated Ironworkers' Association of Australia, where he was briefed by future ALP senator Jim McClelland. He intended to seek Labor endorsement for a parliamentary seat at the 1951 election, but withdrew in favour of another candidate. After the Labor Party split of 1955, however, he became disillusioned with party politics. He disliked what he saw as the Labor Party's leftward trend under Evatt's leadership, but was not attracted to the breakaway group, the Democratic Labor Party. Later in the 1950s, he joined the anti-communist advocacy group established by the United States' CIA, the Association for Cultural Freedom, joining its executive board in 1957.