Spanish coup of March 1939, in historiography often referred to as Casado's coup, was a coup d'état organized in the Republican zone against the government of Juan Negrín. It was carried out by the military with support of the Anarchists and the Socialists; its leader was commander of the Army of the Centre, Segismundo Casado. The conspirators viewed the Negrín government as a hardly veiled Communist dictatorship. Most concluded that the government-endorsed strategy of unyielding resistance against the Nationalists would produce nothing but further deaths and sufferings while the war had already been lost. The military and some politicians intended the coup as a first step towards opening peace negotiations with the Nationalists; for the Anarchists and Socialists the priority was to remove the Communists from power.

Segismundo Casado López was a Spanish Army officer; he served during the late Restoration, the Primo de Rivera dictatorship and the Second Spanish Republic. Following outbreak of the Spanish Civil War he sided with the Republicans, gradually rising to commander of the Army of the Centre. He is best known as leader of the coup against the government of Juan Negrín; its objectives were preventing a Communist takeover and terminating fratricidal bloodshed during the war, considered already lost. The rebels seized control of the Republican zone; in their quasi-government Casado served as the minister of defense. Negotiations with the Nationalists failed; Casado went on exile, first to Britain and from 1947 to Latin America, returning to Spain in 1961.