He was born in Asunción into a prominent family of Juan Andres Gill and Escolástica Garcia del Barrio y Bedoya.

He was the grandson of Don Juan Miguel Gill, one of the founding fathers of Paraguayan Independence and a member of the Cabildo, who had Celtic blood.

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 [1] In 1854 he traveled to Buenos Aires, Argentina where he pursued secondary education and medical training, which he did not complete.

On January 25, 1869 Gill participated in a meeting convened by Don Serapio Machain to petition Allied occupational forces for the establishment of a provisional government.

Among those who attended that meeting were José Segundo Decoud, Cayo Miltos, Carlos Loizaga, Juan Antonio Jara and Salvador Jovellanos, all of whom would soon assume high governmental posts.

During his government he introduced paper currency, created the National College in the Capital and significantly increased taxes; the Civil Code of Argentina was adopted.

Foreign minister Facundo Machaín negotiated and signed the Machaín-Irigoyen Treaty with Argentine Minister Bernardo de Irigoyen under which Paraguay officially ceded Misiones Province, the southern part of the Paraná River and part of Gran Chaco territory, while keeping most of Gran Chaco.

On April 12, 1877 at about 10 in the morning Gill was travelling in the company of his two edecanes (high-ranking officers), down the Villarrica street (currently President Franco str.).

The Colombian poet Dr. Prospero Pereira Gamba (1830–1896), who lived in Argentina as an exile, reflected on this tragic moment experienced by the President in his work "The Spectre".