Jáuregui was born in Lecároz, the son of Matías de Jáuregui and of his wife, Juana María de Aldecoa.
At the age of 25 he entered the military, serving at Cartagena de Indias (now in Colombia) during the British siege in 1740. He rose to the rank of lieutenant general, and became a knight of the Order of Santiago.
Before his appointment as governor of Chile, he also served in Honduras, Puerto Rico and Cuba. In 1772, while resident in Spain, he was named governor by authority of KingCharles III. In October of that year he embarked for Peru with his son Tomás. His wife, a native of Havana whom he had married there, remained in Spain.
Jáuregui was governor of Chile from March 6, 1772, to 1780, during which time he promulgated a number of administrative and governmentalreforms. For example, he set up a postal service on April 29, 1775. He oversaw Chile’s first census, which established the population at 259,646 inhabitants, in 1778.
In June 1772 he introduced a severe ordinance intended to preserve public order. Individuals could not bear arms in public; theft of animals was to be punished by whipping; shopkeepers who did not close at the proper hour were subject to fines. With the agreement of Bishop Alday, he restricted the right of asylum in churches to only two, Santa Ana and San Isidro.
He introduced reforms of the tax-collection system in 1772. For many taxes he ended the farming system (collection by third parties, for a percentage of the revenue), and required that taxes be paid directly to the Crown. This included the customs. The reforms were opposed by the merchants, but Jáuregui put them into effect anyway.
He held a series of formal meeting with indigenous leaders. In April 1774 he met with their ambassadors in Santiago and he met with various leaders in the Parliament of Tapihue the following December. One of the things agreed to was the establishment of a school for the Indigenous, to be run by the Jesuits. This was the Colegio de San Pablo, which opened in April 1775 in Santiago.
Jáuregui presided over the beginning of construction of the cathedral of Santiago, under the direction of the Italian architect he recruited, Gioacchino Toesca. The cathedral was consecrated on December 8, 1775. Also, the Real Universidad de San Felipe enjoyed growth during his tenure. The Academy of Forensic Practice was established, and attached to the University.
In 1776 the Captaincy General of Chile suffered the loss of the province of Cuyo, including the cities of Mendoza, San Juan, and San Luis, due to the creation of the Viceroyalty of the Río de la Plata.
In 1777 Jáuregui established a militia system to defend against rural banditry and prepare for other military action, although each unit was required to finance uniforms and weapons itself. Two cavalry regiments, with 1,400 men, were created, and one new infantry regiment, with 800 men. In the professional army, the forces were redistributed along the frontier in Arauco, and in Santiago. He proposed better pay for the troops, and this was approved by Charles III in January 1778.
By royal order, free trade among various ports in Spain and America was adopted in 1778. Included were Valparaíso and Concepción in Chile. The order also authorized the route around Cape Horn. This was an important benefit for the colony.
Also in 1778 the Colegio de San Carlos was founded in Santiago. This replaced the Convictorio de San Francisco Javier, which had been administered by the Jesuits up until their expulsion.
In May 1778 the Mapocho River flooded.