Sources generally are hostile to Constantine V due to his support for iconoclasm (i.e. nicknaming him 'Kopronymos', or 'dung-named'). After the Council of Hieria (754), Constantine persecuted iconophiles. Nonetheless, he was a capable military leader, campaigning against the Slavs, Bulgarians, and the Arabs.

He repopulated Constantinople after an outbreak of the plague in 747. Most notably, following a drought, he restored the Valens Waterway, including the Valens aqueduct bridge.