Theofilos was against the worship of icons and was in constant dispute with his wife Theodora, who was for the worship of icons (iconolatry). Theofilos was austere and also fair. He did his best to check corruption and oppression on the part of his officials. It is said that when he was informed that a ship had carried in the port of his palace, goods from Syria, Theofilos asked the captain to whom they belonged. The captain answered that they had been ordered by the empress. Theofilos had the ship burnt and told to his wife that whatever she desired, she should go to the market of Constantinople and buy it, because she deprived the taxes and the duties from the State.

On becoming sole emperor in 829, he emulated Harun ar-Rashid by wandering about the capital informally, listening to his subjects' complaints. An intelligent financier and administrator, he dispatched architects and engineers to construct fortresses which would anchor Byzantium's northern defenses against the Vikings and the Magyars. He also constructed a fortress at the Herson peninsula (modern Crimea) to withhold the attacks of asian barbarian tribes. He also bolstered his defenses, east and west, against the Muslims. Theophilus established many local mints, promoting commerce in the regions. His sound fiscal policies greatly enriched the Imperial treasury, and allowed him to embark on numerous building projects. Among these were major expansions to the Great Palace. Despite his interest in their culture, Theophilus was compelled to war with the Muslims throughout his reign. Theophilus, who afforded an asylum to a number of Persian refugees, one of whom, called Theophobus after his conversion to Christianity, married the emperor's sister Helena, and became one of his generals.

On 831, Theofilos sent a delegation to Baghdad, with precious presents for Al-Mamun, signing so a peace treaty which lasted three years. Al-Mamun died in 833 and his successor caliph Al-Mutassem struck at the most important centres of Asia Minor on the route to Constantinople. The emperor organized a huge campaign against the Arabs and marched to Eufrates river, at Mesopotamia. He destroyed many Arab cities and also Sozopetra, the birthplace of Al-Mutassem. Al-Mutassem swore for revenge. With his turn, he organized a huge army of more than 200 thousands men and had them written on their shields, the name Amorion, the capital of Frygia, which was the homeland of the Greek emperor. Theophilus was defeated in a bloody battle at Dasymon, in July 838. His competent general, the Armenian Manuel was killed and the Byzantine army retreated to Amaseia. After a brave resistance of fifty-five days, Amorion fell into Al-Mutassem's hands through treachery on September 23, 838. So one of the empire's chief fortresses and the home of Theophilus' dynasty was razed to the ground and most of the population was slaughtered. The Greek generals Aetios, Krateros, Melissinos, the protospatharios Theodoros, the tourmarhis Kallistos, the througgarios Konstantinos and many other political and military noblemen were captured and tortured to death. The fall of Amorion shocked the Greek populations who for many centuries sung folkloric songs mourning the loss of Amorion, Kastron tis Marous. Exploiting dissension within the Arab camp, however, Theophilus in 841, with the help of Spanish Moors, captured Melitene on the Armenian border, forcing Al-Mutassem to sign a truce.

Under Theophilus, Iconoclasm was given full rein. To weaken the political influence of Greek Orthodox monasticism, the Emperor and Ioannes Grammatikos (who had become patriarch of Constantinople) mounted a persecution against the users of icons in Orthodox liturgy and devotion. Theophilus never recovered from the Arab blow; his health gradually failed, and he died on 20 January 842. His wife, Theodora who had always been iconolatre, restored the legitimacy of venerating icons to the Byzantine Empire. The decision was ratified by a synod on 19 February 842, and Methodios who was iconolater succeeded Grammatikos as Ecumenical Patriarch. Since then, all Orthodox christians celebrate the first Sunday of fast (Sarakosti), as Kuriaki tis Orthodoxias,

The Byzantine cultural revival stimulated by Theophilus included two significant advances in the area of classical studies: the gradual substitution of the minuscule, or smaller, cursive hand for the uncial, or larger, script, and the increase in the number of scriptoria,or copyists' workshops. Theophilus also restored the University of Constantinople after its 8th-century decline and appointed the brilliant Byzantine teacher Leo the Mathematician as its new rector.