As a young man Fulgenzio Micanzio entered the order of the Servants of Maria and studied in Bologna, where he remained as a teacher until 1606. In that same year Paolo Sarpi (1552-1623) requested his support in his struggle against Paul V, which led to the interdiction against the Republic of Venice. After that Micanzio became his disciple and, when Sarpi died, took over his post as theologian and canonical of Venice.

Micanzio also kept up his master's friendship with Galileo, with whom he was in contact from the time of Sidereus nuncius. Their correspondence intensified during the 1630's, and Micanzio stood by Galileo throughout his trial and especially after his condemnation. Micanzio was a precious point of reference for Galileo on that island of freedom which Venice then respresented. It was through Micanzio that Galileo was able, for example, to get the manuscripts of his Discorsi e dimostrazioni sopra due nuove scienze [Discourses and Demonstrations concerning Two New Sciences] (Leiden, 1638) to the Dutch publisher Elzevir, and it was again Micanzio who pressed for a complete edition of Galileo's works, which however did not get off the ground at that time. Micanzio also helped Galileo with certain practical matters, such as securing his ecclesiastical pension, to which he had accrued a right from 1624, or the purchase of an especially prized violin through Claudio Monteverdi (1567-1643), then choirmaster of Saint Mark's cathedral, for his nephew Alberto Cesare.