Born in Sultepec, Mexico on April 14th, 1833 son of Captain Jose Hernandez. He enrolled at the Colegio Militar on September 13th, 1847 where he served in the first company under Captain Domingo Alvarado. Cadet Hernandez fought the war against American invaders that took place at the Chapultepec Castle alongside the soldiers who would become known as the Niņos Heroes. He was taken prisoner along with General Mariano Morterde, director of the Colegio Militar during this campaign and eventually set free. In 1851 he left military school to become a full time artist. He specialized in portraiture and landscapes. Today, the Colegio Militar houses the portraits made by Santiago Hernandez of the Niņos Heroes, hero patriots who died for their country on that fateful battle of Chapultepec.
During the Reform and French Intervention he was a caricaturist for La Orquesta, El Colmillo and El Ahuizote, three widespread periodicals of the time. He also was given a professor position at the Academia Nocturna de Filosofia where he founded several newspapers such as El Perico, El Palo de Ciego and El Espectro. He also made various prints for these periodicals. During Porfirio Diaz's dictatorship, he was persecuted insatiably by the French General Forey because of his satirical views of politicians in the media.
He illustrated several books such as El Libro Rojo (Vicente Riva Palacio), El Episcopado Mexicano, and Historia del Ferrocarril Mexicano. His legacy has continued through the years as he was honored with the name of a school in his native Sultepec which stands to this day.