He was the third son of Peter III of Aragon and served in the War of the Sicilian Vespers on behalf of his father and brothers, Alfonso ΙΙΙ and James ΙΙ.

This communiqué seems to have had in mind Ponç Hug as a recipient, for the count penned a response (under the title con d'Empuria), A l'onrat rei Frederic terz vai dir, in which he praised Frederick's tact and diplomacy, but told him bluntly that he would not abandon his sovereign.

Frederick landed in Calabria, where he seized several towns, encouraged revolt in Naples, negotiated with the Ghibellines of Tuscany and Lombardy, and assisted the house of Colonna against Pope Boniface.

Unfortunately for Frederick, a part of the Catalan-Aragonese nobles of Sicily favoured King James, and both John of Procida and Roger of Lauria, the heroes of the war of the Vespers, went over to the Angevins, and the latter completely defeated the Sicilian fleet off Capo d'Orlando.

[2] For two years more the fighting continued with varying success, until Charles of Valois, who had been sent by Boniface to invade Sicily, was forced to sue for peace, his army being decimated by disease.

In August 1302 the Treaty of Caltabellotta was signed, by which Frederick was recognised king of Trinacria (the name Sicily was not to be used) for his lifetime, and was to marry Eleanor of Anjou, daughter of Charles II of Naples and Maria Arpad of Hungary.

A truce was concluded in 1317, but as the Sicilians had helped the north Italian Ghibellines in the attack on Genoa, and Frederick had seized some Church revenues for military purposes, Pope John XXII excommunicated him and placed the island under an interdict (1321) which lasted until 1335.

The election of Pope Benedict XII (1334), who was friendly to Frederick, promised a respite; but after fruitless negotiations the war broke out once more, and Chiaramonte went over to Robert, owing to a private feud.