Ochino's defection to the Protestants back then would have been tantamount to someone like Fr. Benedict Groeschel or Fr. John Corapi becoming a Protestant Evangelical. Prior to his defection, Ochino was a gifted preacher, a humble Franciscan, and a source of Catholic renewal. It was a very scandalous affair.
A native of Siena, he joined the Observantine Franciscans and rose to be their general. In 1534 he transferred to the still more austere Capuchins, of whom he was twice (in 1538 and 1541) the vicar-general. His preaching was so eloquent and moving that Emperor Charles V said of him, ‘That man is enough to make the stones weep.’
Contact with Peter Vermigli led him to accept Protestant doctrines, and in 1541 he became a Lutheran. He was cited before the Inquistion, but escaped to Geneva. From 1545 to 1547 he was minister to the Italian Protestants at Augsburg.
In the latter year T. Cranmer invited him to England and secured for him a Prebend of Canterbury and a royal pension as an Anglican. In England, Ochino gave himself up to writing The Usurped Primacy of the Bishop of Rome and the Labyrinth, the latter attacking the Calvinistic doctrine of Predestination. On Queen Mary’s accession to the English throne, he returned to Switzerland and in 1555 was appointed a pastor at Zurich, but on account of his Thirty Dialogues (1563), which proved him unsound on the doctrine of the Trinity and on monogamy, he was expelled from his office. He then went to Poland, but was not allowed to remain there, and died in Moravia.
The moral of this story: If you leave the Catholic flock, you never know where you'll end up. Ochino was once the leader of a potent Catholic revival. He ended in heterodoxy. Let this be a warning to all of us.