Viriato Fiallo was the son of Alberto Fiallo Cabral and Ramona Rodríguez Germes (daughter of Fidel Rodríguez Urdaneta, a member of the junta that came to power in 1876).
He was a cousin of the fashion designer Óscar de la Renta Fiallo.
Viriato Fiallo emerged as a great leader in the fall of tyranny when he played the anti-Trujillo feelings and was exalted by their struggles and pristine behavior.
He had been a physician in the mills of the Vicini family and had chaired the Dominican-German Committee.
Fiallo was jailed several times for being an outspoken opponent of the regime of Trujillo, following the death of dictator he founded the National Civic Union (UCN), as a nonpartisan movement whose main objective movement was the oust of the Trujillo family and their associates, converting later the UCN movement into a political party with a view to the presidential elections of 1962.