The impact of the economic crisis that had been gaining momentum in Uruguay from the mid-1950s was first felt by agricultural workers in the country’s northern provinces. Their economic situation was approaching catastrophe. In 1961 the Union of Sugar Workers of the Province of Artigas (UTAA) was formed in the north of Uruguay. It was headed by a lawyer from Montevideo, one of the leaders of the Socialist Party, Raúl Sendic. Unlike other trade unions in the country, whose leadership was effectively controlled by the North American capital, the UTAA began an uncompromising struggle for workers’ rights. In 1962, Raúl Sendic, together with the UTAA sugar cane cutters, organized a march to Montevideo to present the workers’ economic demands to the Uruguayan government. Soon, in order to support the UTAA, a group of young activists from various leftwing parties was formed. They sought to coordinate the actions of the protesters and their political sympathizers and were called “Coordination”. Gradually, the participants in the “Coordination” came to the idea of the need to switch to the methods of armed struggle. In the summer of 1963, they expropriated weapons from a gun club in the town of Nueva Helvecia. This operation, known as the “Swiss gun club”, actually began a new stage in the history of the movement, which resulted in 1965 in the creation of a revolutionary organization that resorted to the tactics of “direct action”. It was the Movement for National Liberation, Tupamaros. The subject of this article is the activities of the radical wing of the non-systemic left opposition in Uruguay in the first half of the 1960s, which in 1965 united into a single organization of Tupamaros. The aim of the article is to show the origin and evolution of the opposition organization through its transition from legal methods of struggle to armed ones, right down to guerilla operations. This work, for the first time in Russian historiography, analyzes the key milestones in the formation and development of the Tupamaros revolutionary movement, and considers the economic and political prerequisites of its emergence.