He wrote articles on foreign affairs for the République Française and Le Temps, and in 1888 was elected conseiller général of his native département, standing as "un disciple fidèle de Léon Gambetta".

While in opposition, Delcassé devoted special attention to naval affairs, and in noted speeches he declared that the function of the French navy was to secure and develop colonial enterprise, deprecated all attempts to rival the British fleet, and advocated the construction of commerce destroyers as France's best reply to England.

[1] On the formation of the second Brisson cabinet in June 1898 he succeeded Gabriel Hanotaux as Foreign Minister, and retained that post under the subsequent premierships of Dupuy, Waldeck-Rousseau, Combes and Rouvier.

In 1898 Delcassé had to deal with the delicate situation caused by Captain Marchand's occupation of the town of Fashoda in the Sudan (the Fashoda Incident) for which, as he admitted in a speech in the chamber on 23 January 1899, he accepted full responsibility, since it arose directly out of the Liotard expedition; and in March 1899 he concluded an agreement with Britain by which the difficulty was finally adjusted, and France consolidated her vast colonial empire in North-West Africa.

Delcassé improved relations between France and Italy: at the same time, he adhered firmly to the alliance with Russia, and in August 1899 made a visit to Saint Petersburg, which he repeated in April 1901.

In June 1900 he made an arrangement with Spain, fixing the long-disputed boundaries of the French and Spanish possessions in West Africa.

Finally, in his greatest achievement, he concluded the Entente Cordiale with Great Britain, covering colonial and other questions which had long been a matter of dispute, especially concerning Egypt, Newfoundland and Morocco.

This arrangement was an important factor in leading Britain to side with France against Germany when World War I started.

On 25 September 1911, as the battleship Liberté was moored in Toulon harbor, an accidental explosion in one of her forward ammunition magazines for the secondary guns destroyed the ship.