How was machiavelli a humanist?

Machiavelli’s realism

Niccolò Machiavelli, whose work derived from sources as authentically humanistic as those of Ficino, proceeded along a wholly opposite course. A throwback to the chancellor-humanists Salutati, Bruni, and Poggio, he served Florence in a similar capacity and with equal fidelity, using his erudition and eloquence in a civic cause. Like Vittorino and other early humanists, he believed in the centrality of historical studies, and he performed a signally humanistic function by creating, in La mandragola (1518; The Mandrake), the first vernacular imitation of Roman comedy. His unswerving concentration on human weakness and institutional corruption suggests the influence of Boccaccio; and, like Boccaccio, he used these reminders less as topical satire than as practical gauges of human nature. In one way at least, Machiavelli is more humanistic (i.e., closer to the classics) than the other humanists, for while Vittorino and his school ransacked history for examples of virtue, Machiavelli (true to the spirit of Polybius, Livy, Plutarch, and Tacitus) embraced all of history—good, evil, and indifferent—as his school of reality. Like Salutati, though perhaps with greater self-awareness, Machiavelli was ambiguous as to the relative merits of republics and monarchies. In both public and private writings—especially the Discorsi sopra la prima deca di Tito Livio (1531; Discourses on the First Ten Books of Titus Livy)—he showed a marked preference for republican government, but in The Prince (1532) he developed, with apparent approval, a model of radical autocracy. For this reason, his goals have remained unclear.

Explanation:

Both Joel and Carlo’s answer are good points about Machiavelli’s life and the complex legacy he left by his life and writings. As to whether he was a humanist or not, my answer would be he was a most typical Humanist for his age but for a post enlightenment and more modern manifestos by contemporary organizations of Humanists he falls far short. Like Joel suggested he was a prototypical student of the humanities (which is why they were called humanists) particularly the classics and using story and characters to speak to his audience rather than a detached academic style. Humanists were to some extent more secular looking for truth and wisdom outside of theological dogma and the holy books. This was especially important for later Humanists who took on the church and most became atheists or agnostics by their critical thinking and being students of science or scientists themselves.