The 1973 Chilean coup d'état (Spanish: Golpe de Estado en Chile de 1973) was a military overthrow of the socialist president of Chile Salvador Allende and his Popular Unity coalition government. Allende, who has been described as the first Marxist to be democratically elected president in a Latin American liberal democracy, faced significant social unrest, political tension with the opposition-controlled National Congress of Chile. On 11 September 1973, a group of military officers, led by General Augusto Pinochet, seized power in a coup, ending civilian rule.

Following the coup, a military junta was established, and suspended all political activities in Chile and suppressed left-wing movements, such as the Communist Party of Chile and the Socialist Party of Chile, the Revolutionary Left Movement (MIR), and other communist and socialist parties. Pinochet swiftly consolidated power and was officially declared president of Chile in late 1974. The Nixon administration, which had played a role in creating favorable conditions for the coup, promptly recognized the junta government and supported its efforts to consolidate power.

Due to the coup's coincidental occurrence on the same date as the 11 September 2001 attacks in the United States, it has sometimes been referred to as "the other 9/11".

In 2023, declassified documents showed that Nixon, Henry Kissinger, and the United States government, which had described Allende as a dangerous communist, were aware of the military's plans to overthrow Allende in the days before the coup d'état. According to historian Sebastián Hurtado Torres, there is no documentary evidence to support that the United States government acted actively in the coordination and execution of the coup actions by the Chilean Armed Forces, however, Richard Nixon's interest from the beginning was that the Allende government would not be consolidated. Historian Peter Winn found "extensive evidence" of United States complicity in the coup.

During the air raids and ground attacks preceding the coup, Allende delivered his final speech, expressing his determination to remain at Palacio de La Moneda and rejecting offers of safe passage for exile. Although he died in the palace, the exact circumstances of Allende's death are still disputed, but it is generally accepted as a suicide.

Chile had previously been regarded as a symbol of democracy and political stability in South America, while other countries in the region suffered under military juntas and caudillismo; the Chilean period prior to the coup is known as the Presidential Republic (1925–1973) era. At the time, Chile was a middle-class country, with about 30% or 9 million Chileans being middle class. The collapse of Chilean democracy marked the end of a series of democratic governments that had held elections since 1932.

Historian Peter Winn described the 1973 coup as one of the most violent events in Chilean history. The coup led to a series of human rights abuses in Chile under Pinochet, who initiated a brutal and long-lasting campaign of political suppression through torture, murder, and exile, which significantly weakened leftist opposition to the military dictatorship of Chile (1973–1990). Nonetheless, Pinochet stepped down from power voluntarily after the internationally supported 1989 Chilean constitutional referendum held under the military junta led to the peaceful Chilean transition to democracy.

Allende contested the 1970 Chilean presidential election with Jorge Alessandri Rodríguez of the National Party and Radomiro Tomic of the Christian Democratic Party. Allende received 36.6% of the vote, while Alessandri was a very close second with 35.3%, and Tomic third with 28.1%, in what was a close three-way election. Although Allende received the highest number of votes, according to the Chilean constitution and since none of the candidates won by an absolute majority, the National Congress had to decide among the candidates.