Born Jan. 17, 1906, in Puerto Saavedra; died July 21, 1949, in Santiago. Figure in the Chilean labor and trade union movement. Member of the Communist Party of Chile (CPC) from 1929.
A peasant by origin, Fonseca became a teacher. In 1923 he founded the Teachers’ Federation, which advocated the democratization of education; he headed the organization until 1934. From 1937 to 1940 he was a leader of the Communist Youth League of Chile. He was actively involved in the Popular Front (1936–41). From 1940 to 1946, Fonseca served on the Political Commission of the Central Committee of the CPC and edited the party’s central organ, El Siglo (The Century). In 1941 he was elected a deputy to the National Congress of Chile. In 1946 he became general secretary of the Central Committee of the CPC.