Constantine V's reign saw a consolidation of Byzantine security from external threats. As an able military leader, Constantine took advantage of civil war in the Muslim world to make limited offensives on the Arab frontier. With this eastern frontier secure, he undertook repeated campaigns against the Bulgars in the Balkans. His military activity, and policy of settling Christian populations from the Arab frontier in Thrace, made Byzantium's hold on its Balkan territories more secure.

Religious strife and controversy was a prominent feature of his reign. His fervent support of Iconoclasm and opposition to monasticism led to his vilification by later Byzantine historians and writers, who denigrated him as Kopronymos or Copronymus (Κοπρώνυμος), meaning the dung-named. The Byzantine Empire enjoyed a period of increasing internal prosperity during Constantine's reign. He was also responsible for important military and administrative innovations and reforms.