John I was Pope from 523 to 526. He was a native of Tuscany, and was very old and frail by the time he was elected to the papacy.

Despite his protests, he was sent by the Arian King Theodoric the Great of the Ostrogoths to Constantinople to secure a moderation of Emperor Justin's decree of 523 against the Arians. Theodoric threatened that if John should fail in his mission, there would be reprisals against the orthodox Catholics in the West.

When Pope John returned to Ravenna, Theodoric's capital, Theodoric had John arrested on the suspicion of having conspired with Emperor Justin. He was imprisoned at Ravenna, where he died of neglect and ill treatment.

His body was transported to Rome and buried in the Basilica of St. Peter.

John I is depicted in art as looking through the bars of a prison or imprisoned with a deacon and a subdeacon. He is venerated at Ravenna and in Tuscany.