The following year he took part in the revolution against Supreme Director Carlos María de Alvear, and later he was sent to Santa Fe Province to control the advance of the federalists.

The day after his arrival governor Francisco Candioti died, which gave Viamonte the opportunity to make the province depend again on Buenos Aires.

In May 1818 he was a deputy to the Congress of Tucumán, and the following year he was named chief of the expeditionary army of Santa Fe, replacing Juan Ramón Balcarce.

Estanislao López immobilized the army directed from Córdoba by Juan Bautista Bustos and captured Viamonte at Rosario, forcing him to sign the armistice of Santo Tomé.

He was exiled to Montevideo after the Battle of Cepeda (1820), but he returned a year later in 1821 and was named governor of Buenos Aires Province due to the absence of Martín Rodríguez.