Gastón de Peralta was appointed viceroy of New Spain in 1566, replacing Francisco Ceinos and the Audiencia Real of Mexico, which had been governing on an interim basis since the death of the previous viceroy, Luís de Velasco.

It was made known to Peralta while he was still at the coast in Veracruz, before he entered Mexico City to take up his office officially.

One of his first acts was to remove the artillery and soldiers that had been posted at the viceroy's palace and in the principal streets of the city.

Alarmed, King Philip dispatched two visitadores, Luis Carrillo and Lic.

In his brief term of office, Peralta founded a hospital for the aged, invalids, convalescents, and the "insane."