John IV (surnamed Jejunator, sometimes also Cappadox) was born at Constantinople of artisan parents, and worked as a goldsmith.

Through the patriarch's fervent prayer, a terrible thunderstorm arose with rain and hailstones so that everyone dispersed in fear and came to realize the inappropriateness of such entertainment.

In 593, John IV was severely blamed by Pope Gregory I for having allowed an Isaurian presbyter named Anastasius, who had been accused of heresy, to be beaten with ropes in the church of Constantinople.

In the case of a presbyter named Athanasius, accused of being to some extent a Manichaean, and condemned as such, Gregory I tried to show that the accuser was himself a Pelagian, and that by the carelessness, ignorance, or fault of John IV, the Nestorian council of Ephesus had actually been mistaken for the Orthodox Council of Ephesus.

26) attributes to him only a letter, not now extant, on baptism addressed to St. Leander, John IV, he says "propounds nothing of his own, but only repeats the opinions of the ancient Fathers on trine immersion".