A secretary of the Sindicatu Mineru Asturianu (the local coal miners' branch of the Unión General de Trabajadores, UGT), and a delegate to the International Miners' Federation. As a prominent labor organizer, Tomás led militias formed by workers during the "Revolution of Asturias" of October 1934, being the president of the new (de facto) state,the Asturian Socialist Republic(5-15 of October).He did the revolution not just to face only the right-wing government,but also the properly Spanish second republic. He subsequently took part in the elections of 1936 as a candidate for the Popular Front, being elected a deputy with the election victory the Front carried.
When the Spanish Civil War erupted, Belarmino Tomás led the miners' militias attacking Oviedo (held by Francisco Franco's forces). He was voted President of the Consejo Soberano de Asturias y León upon its creation on August 24 1937. In Gijón on October 20, the day the city was devastated by Franco's forces, Tomás left for the Republican zone and continued fighting on several fronts, exiling himself when the Popular Front was defeated in early 1939.He was also popular because of the Belarminos, the money that was used in this declarated-state during his presidence.