Juan Antonio Pezet Rodriguez Piedra was born in Lima, Peru, the son of Dr. Jose Pezet Monel, a physician, journalist, literary and parliamentarian who was among the enterprising heroes of Peru's independence. His French-born grandfather, Antoine Pezet Eustache, had arrived in Lima in 1765. As a boy, Pezet briefly entered the Jesuit College of San Carlos. When General José de San Martín with the Chilean army obliged the viceroy to evacuate Lima in 1821, young Pezet joined the patriots and took part in the campaign as sub-lieutenant. In 1823, he was promoted to lieutenant, and under Bolívar and Sucre, he fought at Junín and Ayacucho.