He was chosen by Crescentius and the nobles of Rome, in revolt against the will of the youthful Holy Roman Emperor Otto III, the cousin of Pope Gregory V. John and Gregory were rivals until the council of Pavia in 997.
The revolt of Crescentius was decisively suppressed by Otto III, who marched upon Rome. John XVI fled, but the emperor's troops pursued and captured him, cut off his nose and ears, cut out his tongue, blinded him, and publicly degraded him before Otto and Gregory. He was sent to the monastery of Fulda, in Germany, where he lived until AD 1013.
Although he was not a legitimate Pope, the next Pope John took the regnal number XVII, and the sequencing was never subsequently corrected. Further, there was never a Pope John XX at all. Hence, the most recent John, Pope John XXIII, was in fact only the 21st legitimate Pope of that name.