Cyrus was City Prefect of Constantinople (PUC) for the first time in 426, enjoying the support of Empress Eudokia (wife of Theodosius II). He held the post again in 439-441, while simultaneously bearing the title Prefect of the East (PPO). His literary and building activities made him popular, and he was removed from power and made bishop of Cotyaeum in 443. After the death of Theodosius II in 450, Cyrus returned to secular life in Constantinople.

Cyrus supervised the building of the Baths of Achilles.