John Thomand O'Brien was born in Baltinglass, Wicklow, on the 24th of June 1786. He emigrated to Brazil in 1811 where he attempted to set up several businesses in Brazil and then Argentina. O'Brien's efforts in the commercial domain proved unsuccessful, so he switched his focus to the military when emerging movements in Latin America sought to overthrow Spanish rule.
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He served as adjutant to José de San Martín, who was foundational to the liberation of Argentina, Chile, and Peru from Spanish control. O'Brien participated in San Martín's campaigns in Chile and Peru, and his efforts during The Liberating Expedition of Peru (1820 - 1822) were noted on his return to Buenos Aires.
Following his military activities, O'Brien pursued mining opportunities near the town of Puna, Peru. The mine was located near the shores of Lake Titicaca, high in the Andes, and it was difficult to supply due to its remote location. O'Brien solved the problem by buying a brig in Lima, dismantling it, and transporting it across the Andes on mules. Reassembled, this ship, named the Julia, won fame for O'Brien as the operator of the highest commercial sailship in the world at roughly 3,800 meters or 12,000 feet.
Despite his efforts, O'Brien's mining ventures proved unsuccessful. In the late 1820s, he began a movement encouraging the migration of Irish people to Argentina. While the initial response to his overtures was tepid, the effort laid the groundwork for what was to become the Latin American Irish diaspora, mostly sourced from the central counties of Westmeath, Longford, and Offaly.
In the 1830s, a restless O'Brien left Argentina to explore the Amazon. His subsequent return to Argentina was met with political difficulties with the Juan Manuel de Rosas regime, which led to his imprisonment for a time. He was ultimately released through the intercession of de Rosas' daughter and British diplomatic pressure.
By the 1840s, O'Brien resettled in Uruguay, where in 1848, he was appointed Consul General to the UK. That appointment led to his return to Europe, where he died in Lisbon, Portugal, on the 1st of June 1861. His body was repatriated to Argentina in 1935 and he is buried in the Cementerio de la Recoleta in Buenos Aires.
