The Decouds were historically strong opponents to the López regime, and in the early 1850s the execution of his uncles Teodoro and Gregorio due to treason forced his family into exile.

Together with his brother Juan José, he studied at the Colegio del Uruguay in Entre Ríos, Argentina[4] and later joined the law school at the University of Buenos Aires.

[6] As the war went on, he and his brother started to publish a newspaper called El Nacionalista in Corrientes, in which they harshly denounced the "secret clauses" of the Treaty of the Triple Alliance which would lead to Paraguay losing territory.

[11] Afterwards, as Paraguayan politics took a violent turn,[12] Decoud withdrew temporarily from them to focus on his career as a journalist, and returned only in 1878 as minister for the Candido Bareiro government.

One of his most important feats was achieved in 1885, when he went to London as an extraordinary envoy and managed to renegotiate Paraguay's debt there from little short of 3 million pounds sterling to 850 thousand, though the country had to cede 8,700 km2 of land to the bondholders in exchange.

Decoud also translated Joseph Alden's The Science of Government in Connection with American Institutions to Spanish,[23] and wrote books and articles such as Recuerdos históricos, La amistad, Cuestiones Políticas y Económicas, edited in 1876, and El patriotismo, published in 1905.

Disillusioned with the direction of post-war Paraguayan politics, Decoud committed suicide in 1909, leaving a letter to his wife in which he stated:[25] The citizens of classical antiquity preferred death to a sterile life cut short by the low passions of men.