The political career of Fidel Castro saw Cuba undergo significant economic, political, and social changes. In the Cuban Revolution, Fidel Castro and an associated group of revolutionaries toppled the ruling government of Fulgencio Batista, forcing Batista out of power on 1 January 1959. Castro, who had already been an important figure in Cuban society, went on to serve as prime minister from 1959 to 1976. He was also the first secretary of the Communist Party of Cuba, the most senior position in the communist state, from 1961 to 2011. In 1976, Castro officially became president of the Council of State and president of the Council of Ministers. He retained the title until 2008, when the presidency was transferred to his brother, Raúl Castro, who was vice president. Fidel Castro remained the first secretary of the Communist Party until 2011.

Fidel Castro's government was officially atheist from 1962 until 1992. Cuba attained international prominence under Fidel Castro's rule, for reasons including his staunch belief in communism, his criticisms of other international figures, and the economic and social changes that were initiated. Castro's Cuba became a key element within the Cold War struggle between the United States and its allies versus the Soviet Union and its allies. Castro's desire to take the offensive against capitalism and spread communist revolution ultimately led to the Cuban Revolutionary Armed Forces (Fuerzas Armadas Revolucionarias – FAR) fighting in Africa. His aim was to create many Vietnams, reasoning that American troops bogged down throughout the world could not fight any single insurgency effectively, a position Che Guevara had advocated in the 1960s. An estimated 7,000–11,000 Cubans died in conflicts in Africa.

Castro died of natural causes in late 2016 at Havana. Castro's ideas continue to be the primary foundation and manner in which the Cuban government functions to this day.

On February 16, 1959, Castro was sworn in as prime minister, and accepted the position on the condition that the prime minister's powers be increased. Between 15 and 26 April, Castro visited the U.S. with a delegation of representatives, hired a public relations firm for a charm offensive, and presented himself as a "man of the people". U.S. President Dwight D. Eisenhower avoided meeting Castro; he was instead met by Vice President Richard Nixon, a man Castro instantly disliked. Proceeding to Canada, Trinidad, Brazil, Uruguay, and Argentina, Castro attended an economic conference in Buenos Aires. He unsuccessfully proposed a $30 billion U.S.-funded "Marshall Plan" for the whole region of Latin America.

After appointing himself president of the National Institute of Agrarian Reform (Instituto Nacional de Reforma Agraria - INRA), on 17 May 1959, Castro signed into law the First Agrarian Reform, heavily influenced by Che Guevara, which limited landholdings to 993 acres (4.02 km²) per owner. He additionally forbade further foreign land-ownership. Large land-holdings (formerly mostly US-owned) were broken up and redistributed; an estimated 200,000 peasants received title deeds. However, the private ownership by the peasants was largely fictitious, as the new farms were largely ran by the state. To Castro, this was an important step that broke the control of the well-off landowning class over Cuba's agriculture.

Castro appointed himself president of the National Tourist Industry as well. He introduced unsuccessful measures to encourage African-American tourists to visit, advertising it as a tropical paradise free of racial discrimination. Changes to state wages were implemented; judges and politicians had their pay reduced while low-level civil servants saw theirs raised. In March 1959, Castro ordered rents for those who paid less than $100 a month halved, with measures implemented to increase the Cuban people's purchasing powers. Productivity decreased, and the country's financial reserves were drained within only two years. In 1960 the Urban Reform Law was passed, guaranteeing that no household would pay more than 10% of its income in rent. Those who were retired, sick, or below the poverty line paid less than 10% or nothing. Private landlords were abolished as tenants and subtenants gained titles to their residences. These reduced rents were to be paid to the state over a period of 5 to 20 years, after which the renters would become homeowners; the state was supposed to turn over this income to the former landlords as compensation, but there is disagreement as to how often it did. In the 1970s, plans to abolish rents altogether were reversed, but nonetheless, by 1972 just 8% of families were paying any rent.

Although he refused to initially categorize his regime as 'socialist' and repeatedly denied specifically being a 'communist', Castro appointed advocates of Marxism-Leninism to senior government and military positions. Most notably, Che Guevara became governor of the Central Bank and then minister of industries. Appalled, Air Force commander Pedro Luis Díaz Lanz defected to the U.S. Although President Urrutia denounced the defection, he publicly expressed concern with the rising influence of Marxism. Angered, Castro announced his resignation as prime minister, blaming Urrutia for complicating government with his "fevered anti-Communism". Over 500,000 Castro-supporters surrounded the Presidential Palace demanding Urrutia's resignation, which was duly received. On July 23, Castro resumed his Premiership and appointed the Marxist Osvaldo Dorticós as the new president.

"Until Castro, the U.S. was so overwhelmingly influential in Cuba that the American ambassador was the second most important man, sometimes even more important than the Cuban president."