As an officer he came to the Río de la Plata to fight in Montevideo, Uruguay against the Portuguese.
In 1782 he was sent to explore and pacify the area of the settlements around the Uruguay River by the newly installed Viceroy Juan José de Vértiz y Salcedo.
He founded five towns in present-day Entre Ríos, among them Gualeguay, Concepción del Uruguay and Gualeguaychú.
Rocamora was the governor of three provinces of the Argentine Mesopotamia: Entre Ríos, Corrientes and Misiones.
He was the governor of Misiones when the May Revolution of 1810 installed the first national government in Buenos Aires, and accepted its authority.