He was known as a primary commander at the Battle of Tuyutí and one of the main leaders of the 1868 San Fernando massacre which executed alleged conspirators against President Francisco Solano López.

Hilário Marcó started his career in a newspaper office called the Imprenta del Estado in 1845.

In 1850 though, he became an ensign in the Paraguayan Army within Battalion Nº 1 based in Paso de Patria.

With the rank of captain, Hilario Marcó became the commander of the police force in the Paraguayan capital Asunción in October 1858.

He would later command the firing squad against alleged conspirators of Solano López during the 1868 San Fernando massacre.