He headed a military unit during the second British invasion of the Río de la Plata, and worked at the Buenos Aires Cabildo.

He supported the secretary Mariano Moreno within the Junta, and was moved to the distant city of San Juan when the Morenists were removed from government.

Together with Carlos María de Alvear, he organized the strategy for the downfall of the royalist stronghold in Montevideo, a threat to Buenos Aires during the Argentine War of Independence.

His father was Martín Ramón de Larrea, who was in charge of customs operations in Mataró, and his mother was Tomasa Espeso.

He promoted the role of deputies from Buenos Aires at the Madrid court, to better the representation of the Brazilian viceroyalty and reduce the privileges of peninsular merchants.

In the absence of reinforcements from Spain, viceroy Santiago de Liniers arranged that everyone in Buenos Aires capable of bearing arms should join the resistance against the second invasion.

[1] Larrea's business prospered, and in 1808 the Buenos Aires Cabildo appointed him to oversee a naval patrol to suppress shipments of contraband.

He also participated in the secret meetings of patriots who promoted political change, and joined the 1809 Mutiny of Álzaga, which attempted to depose viceroy Liniers and replace him with a Junta.

[8] In the assembly, Larrea promoted a customs law which taxed most imports, but made exceptions for machines, scientific tools, books, weapons and military supplies.

During this time the Assembly outlawed torture and repealed all noble titles, and also chose the official Argentine National Anthem.

Posadas was concerned about Montevideo, a nearby city which had been under royalist control since the beginning of the war, and a constant threat to Buenos Aires.

Carlos María de Alvear complemented the existing siege of Montevideo with a naval blockade, in which Larrea's expertise was instrumental.

Larrea drafted a report of the nature, costs and strength of the proposed navy, and the captains and sailors that were required, and planned to negotiate with the American William White.

He continued correspondence with Bernardino Rivadavia, and in 1818 he moved to Montevideo, under Brazilian control at that time, and strengthened his contacts in Buenos Aires from there.

He was appointed consul of the United Provinces by governor Manuel Dorrego, and moved back to Bordeaux to strengthen commerce with France.

His business began to fail, and he lived at various times in Montevideo, Colonia del Sacramento and Bordeaux, before returning again to Buenos Aires.