Segundo Blanco was a school teacher and became active in the syndicalist activities after the First World War. He became a member of the National Committee of the Anarcho-Syndicalists (CNT) in the early 1930s and by the outbreak of the Spanish Civil War was seen as one of the leaders of the movement.

In September 1936 Blanco entered the Provincial Council of Asturias and León. He joined the commission on industry and was responsible for the munitions works in the region.

When Asturias fell in 1937 Blanco fled to Madrid. In April 1938 Juan Negrin, prime minister of the Popular Front government, appointed Blanco as minister of public instruction.

After the Republican Army was defeated in March 1939, Blanco managed to escape to Mexico.