He was appointed Supreme Director of the United Provinces of the Río de la Plata after the Argentine Declaration of Independence.

Pueyrredon's father was a French merchant who established himself in Cádiz with his brother, and later in Buenos Aires, where he married his wife, who was of Spanish and partial Irish descent.

María became the head of the family, assisted by Anselmo Sáenz Valiente in business, and withdrew Juan Martín from his studies at the age of 14.

Pueyrredón escaped to Colonia del Sacramento and joined Santiago de Liniers, whose army would eventually defeat the British.

After the May Revolution of 1810, which gave birth to the first local government junta, he was appointed governor of Córdoba, and in 1812 he became the leader of the independent forces and a member of the short-lived First Triumvirate.

In 1815, at the age of 39, he married his 14-year-old second wife María Calixta Tellechea y Caviedes; Rivadavia, Pueyrredón and Chiclana of the First Triumvirate had had her father executed three years before as a member of the royalist conspiracy of Martín de Alzaga.