He was born at Mendoza (then, still a Chilean dependency), the son of Juan Martínez de Soto Rozas and María Prudencia Correa Villegas.

[1] In 1808 he became secretary to the last Spanish governor, Francisco Antonio García Carrasco, and used his position to prepare the nationalist movement that began in 1809.

Under his influence many reforms were initiated, freedom of trade was established, an army was organized and a national congress was called together in July 1811.

Also a feud broke out between Rozas and José Miguel Carrera, who had secured control of Santiago.

In 1812 Carrera succeeded in securing the banishment of his rival, who was forced to retire to Mendoza, where he died on May 16, 1813.