Pedro de Portocarrero arrived in Mexico a short time after the fall of Tenochtitlan, and thus did not take part in the Spanish conquest of the Aztec Empire. He was placed under the command of Pedro de Alvarado and took part in the campaigns of conquest in Oaxaca, Pánuco (Veracruz), and Central America. In July 1524, Pedro de Alvarado appointed Pedro de Portocarrero as a "regidor" (councillor) of the newly founded Spanish settlement of Santiago de los Caballeros de Guatemala, at that time located at the Kaqchikel Maya city of Iximche. Soon afterwards, Portocarrero accompanied Alvarado on his expedition to Cuzcatlan (in modern El Salvador). In August 1526, Alvarado named Portocarrero as one of two "alcaldes" (magistrates) of Guatemala. In the late 1520s Portocarrero was successful in putting down a Kaqchikel rebellion. Shortly after the initial Spanish invasion of Guatemala, Alvarado granted Portocarrero the extensive "encomienda" of Sacatepéquez and Ostuncalco, the largest and most valuable "encomienda" in Guatemala, which incorporated the entire southern Mam Maya region.