He was born in Asunción into a prominent family of Juan Andres Gill and Escolástica Garcia del Barrio y Bedoya. He was grandson of Don Juan Miguel Gill, one of the founding fathers of Paraguayan Independence and a member of the Cabildo, who had Celtic blood. He was married to Maria Concepcion Diaz de Bedoya. His paternal ancestor, John Thomas [El inglés] McGill ("Tomas McGill") was born in Ireland and migrated to Latin America with his brother. The family shortened the surname to "Gill" when dictator José Gaspar Rodríguez de Francia decreed that prefixes in foreign names should not be used anymore