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