He was the first governor of the Entre Ríos Province and fought in the battle of Vuelta de Obligado on the Paraná River.

Mansilla joined the forces of José Gervasio Artigas in 1812, against the Portuguese armies summoned by the royalist Javier de Elío.

He was shot on May 12, 1813, during the attack to the fortress "El Quilombo", and joined back the siege when his injury healed.

[3] He joined the Army of the Andes in 1814, and fought in the battles of Chacabuco and Talcahuano, under the command of José de San Martín.

He also fought the decisive battle of Maipú under the command of Juan Gregorio de Las Heras.

[5] Mansilla became a general in 1826, and marched to the Argentine-Brazilian War under the command of Carlos María de Alvear, operating at Rio Grande Do Sul.

The battle of Vuelta de Obligado harmed a number of ships, but the navy prevailed after a couple of hours.

Mansilla led a charge against French soldiers that tried to land and dismantle the artillery, being hurt in the chest and leaving Juan Bautista Thorne in command.

[9] Mansilla died in Buenos Aires on April 10, 1871, during an epidemic of Yellow Fever in the city.