He joined the county of Toulouse to his appanage of Poitou and Auvergne, on the death, in September 1249, of Raymond VII, whose daughter Jeanne he had married in 1237. He took the cross with his brother, St Louis, in 1248 (the Seventh Crusade) and in 1270 (the Eighth Crusade). In 1252, on the death of his mother, Blanche of Castile, he was joint regent with Charles of Anjou until the return of Louis IX, and took a great part in the negotiations which led to the treaties of Abbeville and of Paris (1258-1259).
His main work was on his own estates. There he repaired the evils of the Albigensian war and made a first attempt at administrative centralization, thus preparing the way for union with the crown. The charter known as "Alphonsine," granted to the town of Riom, became the code of public law for Auvergne. Honest and moderate, protecting the middle classes against exactions of the nobles, he exercised a happy influence upon the south, in spite of his naturally despotic character and his continual and pressing need of money.
He died without heirs on his return from the Eighth Crusade, in Italy, probably at Savona, on August 21 1271.
See B. Ledain, Histoire d'Alphonse, frère de S. Louis et du comte de Poltou sous son administration (1241-1271) (Poitou, 1869); E. Bourarie, Saint Louis et Alphonse de Poitiers (Paris, 1870); A. Molinier, Etude sur l'administration de S. Louis et d'Alphonse de Poitiers (Toulouse, 1880); and also his edition of the Correspondance administrative d'Alphonse de Poitiers in the Collection de documents inedits pour servir à l'histoire de France (Paris, 1894 and 1895).
See also: Counts of Toulouse