Ambrose Bernard O'Higgins was born in Ballinary, County Sligo, (though some sources say County Meath) Ireland, perhaps in 1720. He had an uncle in the priesthood, serving in Cadiz, Spain, away from Protestant British rule in Ireland. Like many other young Irishmen of the time, Ambrose went to Spain for education and advancement not available to them in Ireland. Following his education, Ambrose, now known by the Spanish spelling of his name, Ambrosio, went to South America as a civilian in business, first in Buenos Aires, and then to Lima.
He became involved in opening new roads as an engineer/draftsman and eventually joined the Spanish army in that capacity.
His capabilities saw him rise in responsibility and in 1764, he went to Chile as an assistant to another Irishman, John Garland, who was military governor of Valdivia, a city in Southern Chile. Ambrosio did well, earning the Spanish title of respect of Don Ambrosio.
Ambrosio might well be called "Chile's postal hero, or the Irishman Who Brought the Mail to Chile. On his first harrowing journey over the Andes mountains separating Argentina and Chile during the winter of 1763-64, Ambrose conceived the idea of a chain of weatherproof shelters. By 1766, thanks to O'Higgins' efficient execution of this plan, Chile enjoyed all-year overland postal service with Argentina, which had previously been cut off for several months each winter." (The South American Irish)
At this time, Peru and Chile were not separate nations, but part of the viceroyalty governed from Lima. Don Ambrosio rose equally in military command as in the Spanish colonial service, distinguishing himself in the continuing campaigns against the Araucanians in the southern extreme of the territory, becoming a Cavalry Brigadier and Commander of the Dragoon Corps of Chile, then Governor of Concepción in 1777.
It was at this time that he became acquainted with the powerful Riquelme family, and fell in love with the daughter, Isabel, almost forty years his junior. He promised marriage, but colonial law forbade marriage between public officials and criolla women without authorization of the crown. To disregard this law was to risk career and position. It isn't known why Don Ambrosio didn't seek permission, but no marriage ensued even when Isabel became pregnant. Perhaps her family disapproved of the match. Isabel gave birth to Ambrosio's only son in August of 1778. Two years later, Doña Isabel married Don Félix Rodríguez with whom she had a daughter, Doña Rosa Rodríguez Riquelme.
Subsequently, Don Ambrosio concentrated on his career, becoming next Gobernador y Capitán General del Reino de Chile, Presidente de la Real Audiencia de Santiago, Superintendente Subdelegado de la Real Hacienda and Intendente de la Provincia de Santiago. He focused on developing the resources of the country, with an enlightened policy that accomplished much for Spanish interest, but also paved the way for later events in the country's history.
He founded cities, improved roads, reconstructed the city of Osorno, abandoned due to continual indigenous attacks, and erected dikes along the banks of the Mapocho river which regularly flooded Santiago. He improved communications and trade with other Spanish colonies, based on a growing agricultural base. He abolished the encomienda system whereby natives were forced to work the land for the crown, an act reinforced by royal decree in 1791.
In 1795, in addition to being Teniente General de los Reales Ejércitos, Don Ambrosio was named Barón de Ballenary, and the following year became Viceroy of Peru: Virrey y Capitán General del Reino del Perú and Presidente de la Real Audiencia de Lima.
In 1796, the King of Spain also conferred upon him the title of Marqués de Osorno. He was an able administrator in Peru, turning his attention to civil development, seeing to the final construction of the Cathedral in Lima.
In 1798, Chile was separated from the Viceroyalty of Peru. In 1800, citing Don Ambrosio's advanced age and ill-health, he was relieved of his post and died the following year, at age 81, in Lima. Don Ambrosio never married.