There's no birth certification whatsoever, though Juan De Garay regarded himself as somebody from Biscay (a region from the Basque Country).

He was governor of Asunción (present day Paraguay) and founded a number of cities in present-day Argentina, many near the Paraná River area, including the second foundation of Buenos Aires, in 1580.

The governor of Asunción sent him in April 1573, with a company of eighty men, on an expedition to the Paraná River, during which he founded the city of Santa Fe de la Vera Cruz.

Juan de Garay died near the Río de la Plata while travelling from Buenos Aires to Santa Fe on 20 March 1583; his group of 40 men, a Franciscan priest and a few women, entered an unknown lagoon and decided to spend the night on the banks of the Carcarañá River, near the ancient Sancti Spíritus Fort.

The family had a certain economic and cultural level, it should be kept in mind that his uncle was appointed Judge and "Alcalde Mayor" of Segovia and his cousin attended the University of Salamanca.