In addition to his work as a researcher and teacher in the field of biology, he pursued a political career as part of which contributed to the design of the Statute of Autonomy of Galicia and became mayor of Pontevedra and congressman for the Federación Republicana Gallega in 1931, among other positions. He was general Secretary General of Izquierda Republicana and Commissioner of Defense during the Spanish Civil War. At the end of the war, he went into exile in France and finally in Mexico, where he arrived in 1940 and achieved Mexican nationality in 1941.
In 1938, during the Civil War, Osorio-Tafall was invited to New York by the Frente Popular Antifascista Gallego and the Sociedades Hispanas Confederadas. He arrived in the city on March 21st. The next day he gave a lecture at the venue shared by the Centro Gallego and the FPAG (at 66 Columbus Avenue), where he spoke about the development of the Galicianist movement and the Statute of Autonomy. He also read a letter from Castelao (who at the time was in Barcelona while it was being bombed by the fascists), entitled “To the Galician Anti-fascists of New York”. The letter was also published in the Barcelona magazine Nueva Galicia (22/6/1938) and in New York in La Voz (15/7/1938). On the 25th of the same month, Osorio-Tafall took part in another event at the Central Opera House (205 East 67th Street), in which he defended the position of President Juan Negrín in the fight against Franco. In April 1939 he was appointed secretary general of the SERE (Servicio de Evacuación de los Republicanos Españoles) created by Negrín.
After his stay in New York he left for the Dominican Republic and then Mexico, where he was professor at the Universidad Autónoma. He also held positions in the United Nations, the Sociedad Mexicana de Historia Natural and the Oficina Regional para la Agricultura en Chile, for which he also worked in Indonesia and Egypt. He was awarded the Medalla de Ouro by the Academia Galega das Ciencias in 1987 and the Medalla Castelao en 1988 (Sources: Real Academia de la Historia, “Bibiano Fernández Osorio Tafall”; Emilio González López, Castelao, propagandista da República en Norteamérica (2000); Consello da Cultura Galega, “Repertorio biobibliográfico do exilio galego”; Miguel Anxo Seixas Seoane, Castelao. Construtor da nación, tomo II (1931-1939) (2020)).