Originally a general of Armenian origin. He murdered Nikephoros II and succeeded him as emperor. In the aftermath of the murder, he got rid of Nikephoros' wife empress Theophano who helped him, and he acted in close concord with the church by cancelling his predecessor's legislation against church land ownership. John waged wars against Bulgaria, allied himself with Otto I and fought succesfully in Syria. John died on campaign; according to rumours he had been poisoned by the scheming court eunuch Basil Lekapenos 'the Nothos' (bastard).

During John's reign, the Bath of Leo VI was demolished.