His reign saw the first serious check to nearly 50 years of uninterrupted Islamic expansion, most notably when he successfully defended Constantinople from the Arabs, and the temporary stabilization of the Byzantine Empire after decades of war, defeats, and civil strife.

His calling of the Sixth Ecumenical Council saw the end of the monothelitism controversy in the Byzantine Empire; for this, he is venerated as a saint in the Eastern Orthodox Church, with his feast day on September 3.

[5] The eldest son of Constans II and Fausta, daughter of patrician Valentinus,[10] Constantine IV had been named a co-emperor with his father in 654, almost certainly in Easter (13 April).

[23] If anything the emperor Constans II with this move left the Byzantine capital relatively exposed to the imminent danger of the Arabs, despite the fact that both the empress Fausta and his three sons and co-emperors, Constantine IV, Heraclius, and Tiberius had remained there.

The Arab forays in Anatolia had started already by c. 662/3 in the frontier zone of Melitene shortly after Muʿāwiya had emerged victorious from the internal civil strife in the Caliphate.

However, the numerous Arab armies having wintered at camps were malnourished and soon they were suffering severe famine, whereas the outbreak of a smallpox epidemic decimated them in large numbers forcing Yasīd to lift the siege hurriedly.

Nevertheless, the army and navy remained in Cyzicus from where they engaged in small scale battles and raids in the vicinity of Constantinople and its immediate countryside before they set sail back to Syria around 669/70.

The news of the lifting of the siege had not yet reached Suracuse due to the naval blockade of Constantinople and the fear for the worst possible scenario led a party of the emperor's closest high ranking military office holders to unfold a plot to remove him out of, supposedly, concern for the continuation of the empire.

[23] However, the rebel did not enjoy of pope Vitalian's acceptance and only one part of the army lent to him support, whereas the Byzantine navy under the command of the loyal dignitary named Severus returned to Constantinople.

[25] Meanwhile and from another warfront the Egyptian governor Maslama b. Mukhallad sent his fleet under the command of Muʿāwiyah b. Ḥudayj al-Kindī to attack Sicily in order to undermine the efforts of Constans II to reorganise the empire's position in the West.

[23] In the wake of the Arab siege and his father's relocation to Suracuse where presumably the imperial treasury was also moved and possibly plundered after Constans II assassination, Constantine IV was faced with a surging economic crisis.

Other from devaluating the higher order issues the new emperor opted for reissuing the copper follis of Justinian which meant, the iconographic return aside, four times heavier coin.

The fostering of such a propaganda where he was likened himself to Justinian aimed at glossing his reign with a profound renovatio imperii which he essentially did as the Byzantines from 672 to 680 had gained the offensive and through a series of counter attacks to Egypt and to Syria attained to paralyse the Arab danger.

[20] Constantine presided in person during the formal aspects of the proceedings (the first eleven sittings and then the eighteenth), surrounded by his court officials, but he took no active role in the theological discussions.

[13] His brothers Heraclius and Tiberius had been crowned with him as augusti during the reign of their father,[12] and this was confirmed by the demand of the populace,[31] but in late 681 Constantine had them mutilated by slitting their noses so they would be considered ineligible to rule.