A bricklayer,[1] he joined the anarchist movement and presided over the construction union of Madrid of the Confederación Nacional del Trabajo (CNT).

During the congress celebrated in Zaragoza three months before the beginning of the Spanish Revolution, he was in favor of the most radical, collaborating sectors of the Federación Anarquista Ibérica (FAI).

[2] When the Spanish Civil War exploded he was released, and led a column that put down the uprising in Guadalajara, Alcalá de Henares and Cuenca.

[7] When Juan Negrín refused to surrender to Francisco Franco, Mera decided to support Segismundo Casado, commander of the Republican Army of the center, and Julián Besteiro of the Spanish Socialist Workers' Party to stage a coup d'etat and establish an anti-Negrin, anti-Stalinist National Defence Council (Consejo Nacional de Defensa).

In March 1939 he joined the rising of Casado to accelerate the end of the war and to restrain Communist Party of Spain control of the Republican zone.