At the age of nineteen, Ulloa joined the French Geodesic Mission to the Equator, which established that the shape of the Earth is an oblate spheroid, flattened at the poles, as predicted by Isaac Newton.

The mission took more than eight years to complete its work, during which time Ulloa, in close collaboration with his fellow naval officer Jorge Juan, made many astronomical, natural, and social observations in South America.

Ulloa and Juan also helped to organize the defense of the Peruvian coast against the English squadron of Commodore Anson, after the outbreak of the War of Jenkins' Ear in 1739.

Destined for a naval career, at the age of thirteen Antonio embarked in Cádiz on the galleon San Luis, bound for the port of Cartagena de Indias (in present-day Colombia).

At that time the French Academy of Sciences was organizing a major scientific expedition to Quito, in present-day Ecuador, in order to measure the length of a degree of meridian arc (i.e., latitude) at the equator.

This was part of an effort to determine in the precise figure of the Earth in order to settle the scientific debate between the defenders of René Descartes's physics and those who advocated the newer Newtonian mechanics.

In 1735, Ulloa and another young naval officer, Jorge Juan, were appointed by the Spanish Crown to accompany the French Geodesic Mission to Quito.

[1] The early work of the French Geodesic Mission, led by Charles Marie de La Condamine, was delayed and hindered by lack of cooperation from the local Spanish authorities.

In one of his reports he described, for the first time in the European scientific literature, some of the properties of a metal that he called platina ("little silver") and which he encountered during his inspection the gold panning operations in the Chocó region of what is now Colombia.

In 1745, having finished their scientific labours, Ulloa and Jorge Juan prepared to return to Spain, agreeing to travel on different ships in order to minimize the danger of losing their important samples and records.

[1] In 1749, Ulloa published his Relación histórica del viaje a la América Meridional (Madrid, 1748), which contains a full, accurate, and clear description of the greater part of South America geographically, and of its inhabitants and natural history.

[9] Shortly after their return to Spain, Juan and Ulloa penned a confidential report to their political patron, the Marquess of Ensenada, on the state of the defenses and administration of the Spanish domains in South America.

[1] Following Britain's victory of the French and Spanish in the Seven Years' War, France agreed in the 1762 Treaty of Fontainebleau to cede to Spain its colony of Louisiana.

Between 1776 and 1778, in the context of the Spanish support for the rebellion in North America against British rule, Ulloa helped organize a war fleet in New Spain (present-day Mexico).

During the return voyage, he observed the total solar eclipse of 1778, a subject on which he corresponded with the French astronomer Pierre Charles Le Monnier.

Ulloa's fleet met with little success in that mission and he left for Spain ten days earlier than instructed, due to lack to supplies and the poor condition of some of his ships.

The previous events in the Azores led to formal charges of dereliction of duty against Ulloa and two captains under his command, Pedro de Leyba and Manuel Núñez Gaona.

The drawn-out proceedings ended with their definitive acquittal by the Consejo Supremo de Guerra (the supreme court of military justice for the Spanish Empire, presided by King Charles III) in February of 1782.

The Noticias secretas paints a dire picture of the state of the administration of the Spanish dominions in America in the 1730s and 1740s, alleging many instances of official corruption and mismanagement by both the civil and the ecclesiastical authorities, and denouncing the exploitation of the Native American population by unscrupulous governors and priests.