After completing his studies he was sent to Upper Peru, where he was part of the Chuquisaca Revolution of May 25, 1809, first movement against Spanish rule held in the Viceroyalty of the Río de la Plata.

[2] There he was promoted to general and confronted Martin Miguel de Guemes, leader by the way he was carrying on the Guerra Gaucha, successful defensive strategy of defending northern border, but very expensive for the province, especially for high classes.

In the mid-1817 he was named provincial commander of the army of Cordoba in almost permanent struggle with small groups of rebels gauchos, no positive results against the feds.

On 6 December 1820, Arenales led troops into the Battle of Pasco (es), using thick snowfall to launch a surprise attack.

Upon news that royalist forces were defeated by Arenales' expedition, the city of Huánuco called for a town meeting on 9 December 1820.