He was born at Cittadella, 20 km (12 mi) north of Padua, then part of the Republic of Venice.
Protestants of the early modern period used his case as an example of the dreadful consequences of the sin against the Holy Ghost: he discerned evangelical truth, but denied and abjured it for external reasons.
Spiera had a respected position in his native town and a fine house, in which ten children grew up.
On returning home, so he related it himself, "the Spirit", or the voice of his conscience, began to reproach him for having denied the truth.
The treatment was in vain, and the conflict, which Pier Paolo Vergerio and others witnessed, ended in his death, shortly after his return to his home.