He was the son of the Count Annibale, member of the Saliceto branch of the noble family of Visconti, and of Lucia Sauli of Genoa.

Returned to Rome, he was appointed Auditor of the Apostolic Camera by Pope Sixtus V.[5] The new Pope Gregory XIV, a distant relative, on 15 April 1489 appointed Alfonso as Apostolic Nuncio to the Emperor,[4] and already on 4 July of that year he arrived in Prague where Emperor Rudolf II kept his court.

[4] Pope Gregory XIV made him Bishop of Cervia on 8 February 1591 with the idea of sending him as Nuncio in Spain.

Following the instructions of the Pope, Alfonso urged Sigismund Báthory to reconcile himself with the Emperor Rudolf II, and supported his cavalry with huge amounts of money.

[6] From 10 September 1601 until his death, Alfonso Visconti served as Bishop of Spoleto and from 1604 to 1607 as Cardinal Protector for the Austrian hereditary lands.