He led an ill-fated military campaign in Upper Peru. He graduated as a lawyer from the University of Charcas , in Upper Peru.
His cousin, Manuel Belgrano , introduced him to the public administration of the Viceroyalty of the Rio de la Plata. He led the Buenos Aires patriots during the May Revolution, which ended with the removal of viceroy Baltasar Hidalgo de Cisneros from power. He is known as the "Speaker of the Revolution" for his speech during the open cabildo held in Buenos Aires on May 22, He succeeded, and ordered the execution of Liniers and his supporters.
He then commanded the establishment of a revolutionary government in Upper Peru today's Bolivia with the aim of freeing the indigenous peoples and African slaves. In Castelli signed a truce with the Spanish in Upper Peru, but they betrayed him and caught the Northern Army unprepared. As a result, the Argentines suffered a major loss in the Battle of Huaqui on June 20, When Castelli returned to Buenos Aires, the First Triumvirate imprisoned him for losing the battle, and Castelli died shortly afterwards from tongue cancer.
Castelli was born in Buenos Aires in He focused on studying philosophy and theology, but when his father died in , he abandoned his career in the priesthood, for which he felt no strong vocation. There, he learned about the ongoing French Revolution , and the new ideas of the Age of Enlightenment. Castelli returned to Buenos Aires and established a legal firm in his family home.
Like many other nineteenth century Argentines prominent in public life, he was a freemason. The intellectuals of the viceroyalty received and secretly distributed a copy of the Declaration of the Rights of Man and the Citizen , promulgated by the French Revolution in Belgrano and Castelli shared similar ideas about the Spanish trade monopoly and the rights of the natives. Belgrano attempted to appoint Castelli as interim Secretary of the Consulate as his assistant, but faced strong opposition from the peninsular merchants, who delayed the appointment until Belgrano became ill during his stay in Europe, which forced him to take extended leaves from work, and wanted Castelli to be his successor if he resigned.
