The betrayal thesis is an interpretation of the Cuban Revolution that supposes that the revolution was the culmination of a democratic resistance to the dictatorship of Fulgencio Batista. After the success of the revolution in 1959, the rebel leader Fidel Castro began to consolidate political power, and associate with communist officials. This political turn is considered a "betrayal" of the original ethos of the revolution, according to proponents of the betrayal thesis.

The betrayal thesis was developed in the early 1960s, in the immediate aftermath of the Cuban Revolution. It was propagated by Cuban exile organizations such as the Cuban Democratic Revolutionary Front, and the Cuban Revolutionary Council. The thesis was also famously propagated by anti-Stalinist historian Theodore Draper.

In 1953, Fidel and Raúl Castro gathered 70 fighters and planned a multi-pronged attack on several Cuban military installations. On 26 July 1953, the rebels attacked the Moncada Barracks in Santiago and the barracks in Bayamo, only to be decisively defeated by the far more numerous government soldiers. During Castro's court trial for the attack, Castro presented a speech that contained numerous evocations of the "father of Cuban independence" José Martí, whilst depicting Batista as a tyrant. According to Castro, Batista was a "monstrum horrendum ... without entrails" who had committed an act of treachery in 1933 when he initiated a coup to oust Cuban president Ramón Grau. Castro went on to speak of "700,000 Cubans without work", launching an attack on Cuba's extant healthcare and schooling, and asserting that 30% of Cuba's farm people could not even write their own names.

In Castro's published manifesto, based on his 1953 speech, he gave details of the "five revolutionary laws" he wished to see implemented on the island:

After being exiled, Castro formed the 26th of July Movement, and returned to Cuba to overthrow Batista by guerilla war. The beliefs of Fidel Castro during the revolution have been the subject of much historical debate. Fidel Castro was openly ambiguous about his beliefs at the time. Some orthodox historians argue Castro was a communist from the beginning with a long-term plan; however, others have argued he had no strong ideological loyalties. Leslie Dewart has stated that there is no evidence to suggest Castro was ever a communist agent. Levine and Papasotiriou believe Castro believed in little outside of a distaste for American imperialism. As evidence for his lack of communist leanings they note his friendly relations with the United States shortly after the revolution and him not joining the Cuban Communist Party during the beginning of his land reforms.

At the time of the revolution the 26th of July Movement involved people of various political persuasions, but most were in agreement and desired the reinstatement of the 1940 Constitution of Cuba and supported the ideals of Jose Marti. Che Guevara commented to Jorge Masetti in an interview during the revolution that "Fidel isn't a communist" also stating "politically you can define Fidel and his movement as 'revolutionary nationalist'. Of course he is anti-American, in the sense that Americans are anti-revolutionaries".

The Cuban Revolution succeeded in overthrowing Batista on January 1, 1959. A provisional government was established soon after. Fidel Castro held de facto veto power during the process of establishing a provisional government. This de facto power came from his position as commander-in-chief of the rebel army. Immediately after the rebel army seized power, Castro and other rebels agreed to place Manuel Urrutia Lleó as President of Cuba.

In a speech delivered in April 1959, Fidel Castro announced the postponement of the elections promised, which were scheduled to occur after the overthrow of Fulgencio Batista. Castro announced this electoral delay with the slogan: "revolution first, elections later". The announcement was the beginning of an electoral delay that culminated in the solidification of Fidel Castro's rule over Cuba.