Member of the Communist Party and representative of the Federación de Trabajadores de la Enseñanza (FETE-UGT) and the Internacional de Trabajadores de la Enseñanza (ITE). During the Spanish Civil War in 1937, he fled to Portugal, and after a short stay went to France as a stowaway and without any documentation on the ship Masilia. But only a few days after his arrival he traveled to Valencia to join the Republican zone, where he met again with Castelao. In Valencia, he joined other Galicians defending the Republic in the Vodka café, where they created Solidaridade Galega Antifeixista (of which he was secretary), which was later moved to Barcelona. In this city he also directed the magazine Nueva Galicia.
In 1938, he accompanied Castelao on his tour of the United States and Cuba in favor of the Republic. Soto explains Castelao’s visit differently to Emilio González López. According to González López, Castelao was invited by the Sociedades Hispanas Confederadas and the Frente Popular Antifascista Gallego in New York, which also paid for the trip. Castelao would therefore be the first person invited directly by the FPGA, while other trips such as those of Bibiano Fernández Osorio-Tafall had been funded by the government of Juan Negrín. On the contrary, in Soto’s version, Castelao’s journey was devised by President Negrín, who suggested to Castelao the convenience of making a propaganda tour in the American continent. Castelao expressed his desire to start in the United States, as he knew that anti-fascism was prevalent among Spanish migrants who were in this country.
Also according to Soto’s testimony, the Galicians who were in the front of the Ebro and Barcelona agreed that Castelao (who already suffered from health problems, especially affecting his sight) would need to travel with a companion, and that it was Castelao himself who chose Soto for the task. Miguel Anxo Seixas Seoane suggests that Soto’s role could have been imposed by the government or the communists to monitor Castelao or take advantage of his visit.
However, Soto did not travel at the same time as Castelao and Virxinia Pereira, as he had to represent FETE at an international anti-fascist congress chaired by Winston Churchill and held in Paris. Therefore, Soto arrived in New York two days after Castelao, on the Normandie, in June 1938. Under the auspices of the FPAG, Soto accompanied Castelao to his rallies in New York, the United States and Cuba. After the tour, he lived in 230 West 97 Street. Soto also gave speeches on his own and was invited to Tampa by the branch of the FPAG from this city. Castelao and him were named honorary presidents of the FPAG.
Although the next step would be to travel with Castelao to Buenos Aires, Soto accepted the invitation of Mexican President Lazaro Cardenas to organize the Fifth American Congress of Teachers. Mexico would be the final destination of his exile, where he was one of the promoters of the emblematic magazine Vieiros, continuing the journalistic work that he had begun before the Civil War in publications such as La República, El Soviet, Ateo and Escuela del Trabajo, and El Magisterio Español and Nueva Galicia during the war. Despite returning to Galicia in the 1960s to contribute to the refoundation of the UPG (Unión do Povo Galego), he returned to Mexico, where he spent the last years of his life (Sources: Luís Soto, Castelao, a UPG e outras memorias (1983); Emilio González López, Castelao, propagandista da República en Norteamérica (2000), Ana González, “Luís Soto y su comprometido exilio gallego” (2011); Miguel Anxo Seixas Seoane, Castelao. Construtor da nación, tomo II (1931-1939) (2020)).