Sebastian San Vicente was born at Gernika (Guernica) in the Basque country in 1896 (or according to other sources in Gijon in Asturias) into a well off family. He broke with his comfortable background and became a stoker and boiler mechanic in the Spanish Merchant Navy. He was fluent in Castilian, Basque, English and French. He may have been involved in revolutionary activity in Spain, and this may have had something to do with his move to the USA. He lived for a time in New York where he was linked to the IWW. During the Red Scare of 1919 he was accused of attempting to dynamite the Mayflower, the presidential yacht used by Woodrow Wilson. To avoid arrest he fled to Cuba. Here he set up a secret group called Soviets. He was implicated in sabotage against merchant ships and with a pending trial set up an IWW section in Matanzas. He illegally entered Mexico in 1920 or 1921 at Tampico. Here together with fellow anarchist Jose Rubio, originally from Asturias, he organised the Locales Comunistas Libertarios (Libertarian Communist Locals) in Tampico and Orizaba. He was a founder of the Confederación General de Trabajadores (CGT),a revolutionary syndicalist union, and as delegate of Los Hermanos Rojos was elected as its sub secretary (Hermanos Rojos- Red Brothers -was a specific anarchist grouping set up by among others the close associate of the Magon brothers, Librado Rivera, founded in 1917 at Dona Cecilia). In this post he built up the CGT in Atlixco, and was often involved in armed confrontations with bosses, scabs and priests.

He was arrested by the Obregon regime in May and put in a prison at Queretaro and then spent a week in the prison at Manzanillo (he was arrested along with another man of many names, Charles Phillips (aka Jesus Ramirez aka Frank Seaman aka Manuel Gomez aka Charles Shipman) a socialist who had fled military service to come to Mexico in 1918. Phillips had joined the Communist Party. San Vicente appears to have worked with Phillips in the Profintern (at this time there was close cooperation on an international level between anarchists and Bolshevik Communists, as the true nature of the regime had not been widely revealed outside the Soviet Union). Both were expelled to Guatemala at the end of 1921 thanks to intervention of friends in government. Sebastian returned secretly to Mexico two months later after working with Phillips to organise the workers movement in Guatemala.

He was denounced by the Communists following a violent ideological conflict within the Bakers Union of the CGT between the Communists and anarchists. Under the alias of Pedro Sanchez he actively took part in the strike of Palacio de Hierro and the strike of the Federacion de la Compania de Tranvias de Mexico (tram workers). On one occasion he was detained but not recognised and subsequently freed. In April 40 police invaded the CGT h.q. and he had to make his escape through a window. He was detained again in July and then moved to Veracruz. On 16th July 1923 he was deported to La Coruna.

There are reports that he died fighting in a CNT column near Bilbao in 1938.