Bareiro benefited from the opening to the world which was initiated by the regime of Carlos Antonio López, with a group of other Paraguayan students on June 2, 1858, he sailed to Europe, where in London he finished his studies.

The Uruguayan writer Jose Carranza Sienra, who met him at the start of the Paraguayan War, said of Bareiro: ... he has a clear talent, an illustration of anything vulgar, a simple and sympathetic look On March 21, 1864, government appointed Cándido Bareiro as chargé d'affaires in the Paraguayan Embassy in London and Paris.

He was relieved from his post in October 1867 due to inability to organize critically needed armament shipments to Paraguay.

After this decision, the Decoud-Quijarro treaty was signed on 15 October 1879 that recognized Bolivia's claims to northern Chaco, but it was never ratified.

After Bareiro's death his vice-president Adolfo Saguier was prevented from assuming the presidency by a bloodless coup led on September 4, 1880, by Bernardino Caballero.

Lopez ordered to delegate Benitez to Peru and to express the declaration of repudiation by the Paraguayan government towards the treaty of the Triple Alliance.

[citation needed] It is said that one of the mistakes of Lopez was to choose Bareiro as Chargé d'affaires of Paraguay in Europe.

Some accused him of the defeat of Paraguay in the war, since his mission was to travel to Europe to buy weapons, but these were lost because of his incompetence.