An authoritarian military dictatorship ruled Chile for almost seventeen years, between 11 September 1973 and 11 March 1990. The dictatorship was established after the democratically elected socialist government of Salvador Allende was overthrown in a coup d'état backed by the United States on 11 September 1973. During this time, the country was ruled by a military junta headed by General Augusto Pinochet. The military used the breakdown of democracy and the economic crisis that took place during Allende's presidency to justify its seizure of power. The dictatorship presented its mission as a "national reconstruction". The coup was the result of multiple forces, including pressure from conservative groups, certain political parties, union strikes and other domestic unrest, as well as international factors.

The regime was characterized by the systematic suppression of political parties and the persecution of dissidents to an extent unprecedented in the history of Chile. Overall, the regime left over 3,000 dead or missing, tortured tens of thousands of prisoners, and drove an estimated 200,000 Chileans into exile. The dictatorship's effects on Chilean political and economic life continue to be felt. Two years after its ascension, neoliberal economic reforms were implemented in sharp contrast to Allende's leftist policies. The government was advised by the Chicago Boys, a team of free-market economists educated in the United States. Later, in 1980, the regime replaced the 1925 Constitution with a new constitution in a controversial referendum. This established a series of provisions that would eventually lead to the 1988 Chilean national plebiscite on October 5 of that year.

In that plebiscite, 55% of voters rejected the proposal of extending Pinochet's presidency for another eight years. Consequently, democratic presidential and parliamentary elections were held the following year. The military dictatorship ended in 1990 with the election of Christian Democrat candidate Patricio Aylwin. However, the military remained out of civilian control for several years after the junta itself had lost power.

There has been a large amount of debate over the extent of US government involvement in destabilising the Allende government. Recently declassified documents show evidence of communication between the Chilean military and United States officials, suggesting covert US involvement in assisting the military's rise to power indirectly. According to the historian Sebastián Hurtado, there isn't documentary evidence to support that the United States Government acted actively in the coordination and execution of the September 11 coup actions by the Chilean Armed Forces, however, Richard Nixon's interest from the beginning was that the Allende government would not be consolidated and acted actively and decisively in the campaign to destabilize his government. Some key figures in the Nixon administration, such as Henry Kissinger, used the Central Intelligence Agency (CIA) to mount a major destabilization campaign.

As the CIA revealed in 2000, "In the 1960s and the early 1970s, as part of the US Government policy to try to influence events in Chile, the CIA undertook specific covert action projects in Chile ... to discredit Marxist-leaning political leaders, especially Dr. Salvador Allende, and to strengthen and encourage their civilian and military opponents to prevent them from assuming power". The CIA worked with right-wing Chilean politicians, military personnel, and journalists to undermine socialism in Chile. One reason for this was financial, as many US businesses had investments in Chile, and Allende's socialist policies included the nationalization of Chile's major industries. Another reason was the propagandized fear of the spread of communism, which was particularly important in the context of the Cold War. The rationale was that US feared that Allende would promote the spreading of Soviet influence in their 'backyard'. As early as 1963, the U.S. via the CIA and U.S. multinationals such as ITT intervened in Chilean politics using a variety of tactics and millions of dollars to interfere with elections, ultimately helping plan the coup against Allende.

On 15 April 1973, workers from the El Teniente mining camp had ceased working, demanding higher wages. The strike lasted 76 days and cost the government severely in lost revenues. One of the strikers, Luis Bravo Morales, was shot dead in Rancagua city. On June 29, the Blindados No. 2 tank regiment under the command of Colonel Roberto Souper, attacked La Moneda, Chile's presidential palace. Instigated by the neo-fascist organization Fatherland and Liberty, the armoured cavalry soldiers hoped other units would be inspired to join them. Instead, armed units led by generals Carlos Prats and Augusto Pinochet quickly put down the coup attempt. In late July, 40,000 truckers, squeezed by price controls and rising costs, tied up transportation in a nationwide strike that lasted 37 days, costing the government US$6 million a day. Two weeks before the coup, public dissatisfaction with rising prices and food shortages led to protests like the one at the Plaza de la Constitución which had been dispersed with tear gas. Allende also clashed with Chile's largest circulation newspaper, the CIA-funded El Mercurio. The newspaper was investigated for tax evasion and its director arrested and interviewed. The Allende government found it impossible to control inflation, which grew to more than 300 percent by September, further dividing Chileans over the Allende government and its policies.

Upper- and middle-class right-wing women also played a role in the opposition against the Allende government. They co-ordinated two prominent opposition groups called El Poder Feminino ("female power"), and Solidaridad, Orden y Libertad ("solidarity, order, and freedom"). The women carried out the ‘March of the Empty Pots and Pans’ in December 1971.

On August 22, 1973, the Chamber of Deputies passed, by a vote of 81 to 47, a resolution calling for President Allende to respect the constitution. The measure failed to obtain the two-thirds majority in the Senate constitutionally required to convict the president of abuse of power, but the resolution still represented a challenge to Allende's legitimacy. The military viewed themselves as guarantors of the constitution and elements within the armed forces considered that Allende had lost legitimacy as Chile's leader. As a result, reacting to demand for intervention from opponents of the government, the military began planning for a military coup which would ultimately take place on September 11, 1973. Contrary to popular belief, Pinochet was not the mastermind behind the coup. It was, in fact, naval officers who first decided that military intervention was necessary to remove President Allende from power. Army generals were unsure of Pinochet's allegiances, as he had given no prior indication of disloyalty to Allende, and thus was only informed of these plans on the evening of 8 September, just three days before the coup took place. On 11 September 1973, the military launched a coup, with troops surrounding La Moneda Palace. Allende died that day of suspected suicide.