Celio was born in Cirié, near Turin, in Piedmont, now northwest Italy. During much of his lifetime his native district ravaged by a series of wars fought between Charles V, the Holy Roman Emperor and the King of Spain, and Francis I, the King of France. With war came the bubonic plague, a disease which killed many members of his family. He was the youngest of 23 children of Jacomino Curione, a civic official in nearby Moncalieri. His mother, Charlotte de Montrotier, died giving him birth. Celio was raised in Moncalieri until his father died. Then, at age 9, he was sent to live with his Aunt Maddalena in Turin. At the University of Turin he studied oratory, poetry, history, and law.

A manuscript family Bible was Celio's principal inheritance from his father. That his father, prior to the Reformation, owned such a Bible may indicate that some members of the family had been unorthodox, possibly Waldensians. (Arising in the Middle Ages, the Waldensians disputed papal authority and claimed the Bible as the sole guide to faith. Although suppressed in most places, they found a refuge in Piedmont.) After reading the Pauline epistles, Celio began to enquire about the teachings of Martin Luther. He obtained some of Luther's writings from the local Augustinian Friars and also read works of Desiderius Erasmus, Ulrich Zwingli, and Philip Melanchthon. Shortly after he set out, with a couple of friends, on a trip to Germany to meet these Reformers, he was arrested on suspicion of heresy and imprisoned for two months. After he was released, his family sent him to the convent of San Benigno for supervised study. These studies were cut short when it was discovered that he had removed the saint's bones from a reliquary and replaced them with a Bible. He left a note which said, "This is the ark of the covenant, from which the genuine oracles of God may be learned, and in which are contained the true relics of the saints."

Curione fled to Milan where he studied law and taught. The city, occupied by imperial troops, was suffering from famine and plague. Although many others had fled to the countryside, Curione remained and rallied the clergy to face the emergency, distributed food to the poor, and helped to bury victims of disease. Around 1530 he married Margherita Bianca Isacchi, daughter of the family with whom he was living, who had been impressed by his selfless behavior. They had nine children.

Curione next taught at Casale in the Duchy of Montferrat, 1533-36. In 1536, after plague had killed all but one of his remaining siblings, he traveled to Turin, hoping to receive a portion of his father's estate. By threatening him with the Inquisition, his sister and brother-in-law forced him to retreat to the countryside. While waiting for news of his inheritance, and serving as a tutor in a nearby village, he made the mistake of defending Luther in a heated debate with a Dominican preacher. This led to another imprisonment in Turin. He might have been turned over to the Inquisition had he not escaped. According to his story, he tricked the guards into fettering a false foot that he had contrived. He fled to Salň, in Milanese territory. Beginning in 1538 he taught at the university in Pavia, also in the Duchy of Milan. Here, to prevent his arrest by the Inquisition, he was escorted by a body of students wherever he went. Papal pressure on the city government eventually forced him to flee to Venice.

Thanks to the scholar Fulvio Morato, whom he had befriended and converted to Protestantism in Casale, Curione found refuge at the court of the Protestant sympathizer, Renée of France, the Duchess of Ferrara. There he served as teacher and mentor to his friend's daughter, Olympia Morata (1526-55), who became a celebrated writer, scholar, and theologian. Years later, after her death, he gathered and published her works.

In 1541 Curione was engaged as a tutor in Lucca, a republic that briefly flirted with independence from Papal religious control. The following year the civic authorities advised him that if he did not soon leave they would be compelled to send him to Rome. He moved on to Pisa, where he worked briefly as a teacher. Soon, however, an order came from Rome to arrest "a terrible person called Celio from Turin." This time he fled Italy altogether and went to Switzerland.

In 1542 the leader and pastor of the Zurich church, Heinrich Bullinger, obtained a post for Curione as principal of a school in Lausanne. While fetching his family from Italy he narrowly avoided capture by the Inquisition. According to his version of the story, when the arresting officer confronted him at dinner at an inn, he stood up, carving knife in hand. Confronted with imagined deadly resistance, the official fainted. In Switzerland Curione was known as a great raconteur of his picaresque adventures in Italy.

Curione lost his Lausanne job in 1546, when he was caught having an affair with a female student. With the help and support of Martin Borrhaus, Professor of Old Testament in Basel, and Jerome Froben, the prominent Basel publisher, in 1547 Curione was appointed Professor of eloquence at the University of Basel. Here he remained the rest of life, teaching and publishing textbooks on rhetoric, histories, translations, and annotated editions of the classics. Such was his celebrity as a scholar that he received tempting offers from the Prince of Transylvania, the Emperor Maximillian II, and the Duke of Savoy. The Pope promised him immunity from the Inquisition if he moved back to a Roman Catholic domain and held his peace on religious matters. But Curione had no desire to once again put himself at hazard. He only barely avoided serious trouble with Protestant authorities in Switzerland.

As a professor, Curione was expected to provide room and board for foreign students. He attracted to Basel students who, before the political climate changed in Italy, would have studied in Padua. In 1547 Lelio Sozzini (Laelius Socinus) stayed with him. A few years later, at the time of the trial of Servetus, 1553, he hosted several Polish students.

After Servetus was burned at the stake, Curione contributed to an underground movement protesting the execution and attempting to rehabilitate Servetus's controversial views. He denied composing a set of satiric verses, "Epitaphium Michaelis Serveti." These were attributed to him in part because he had earlier composed a book of poetic satires on the Roman Catholic clergy and nobility, Pasquino in Ecstasy (Pasquillus ecstaticus), 1544. It is likely that he at least helped to spread the pro-Servetus verses. He and Sozzini helped Castellio prepare the pseudonymous Should Heretics be Persecuted? (De haereticis, an sint persequendi), 1554, an anthology of passages in favor of religious toleration. One short passage in the book was taken from his tract, A Defense of the True and Ancient Authority of Christ's Church Against Antony Florebell (Pro vera et antiqua Ecclesiae Christi autoritate in A. Florebellum Mutinensem Oratio), 1550.

Under the pseudonym Alphonsus Lyncurius Tarraconensis, Curione, together with Gribaldi, and possibly Sozzini as well, wrote Apologia pro Michaele Serveto, 1554. He may also have helped Gribaldi and Sozzini to manufacture A Declaration concerning Jesus Christ, the Son of God (Declarationis Jesu Christi filii dei), a pastiche work which they credited to Servetus. "Lyncurius" added a preface. Declarationis, which was never published, came to the attention of the Protestant authorities in 1559, when one of Curione's former students, Michael Zaleski, was murdered in Tübingen, Germany. The manuscript was found amongst Zaleski's effects. The Italian Reformer, Pier Paolo Vergerio, conducted the subsequent investigation. "Celio is very much suspected," he wrote, "of having compiled several writings of Servetus in a single volume together with a preface."

Many of Curione's avowed religious writings were fairly orthodox from a Protestant point of view. Of the four religious essays published as Opuscula, 1544, only the last, "On the Prologue to the Gospel of John," was at all heretical. The Christian Institutes (Christianae religionis institutio), 1549, was unexceptionable, except in that it neglected to mention the Trinity. The work that got Curione into the most trouble was On the Great Extent of God's Blessed Kingdom (De amplitudine beati regni dei), 1554. In this he called the doctrine of election "a biased, hateful, and malicious belief, calculated to drive souls to despair" and contended that the number of people who would be saved was much greater than most people imagined, most of humankind. He also claimed that many could achieve salvation by observing natural law, without converting to Christianity. Because he knew that the book would be controversial, and possibly dangerous to himself, he delayed publishing it for seven years and ultimately had it published away from Basel, in Poschiavo in the canton of Grisons (Graubünden) in southeast Switzerland. It was dedicated to King Sigismund II of Poland. In 1557, when Vergerio found that De amplitudine was circulating in Poland, he tried unsuccessfully to have it condemned.

In 1557 Curione's friend Gribaldi, under suspicion of Antitrinitarianism, fled his post at the University of Tübingen. Vergerio discovered a incriminating unorthodox manuscript, critical of Calvin and other Reformers, that contained editorial corrections in Curione's handwriting. Curione protested that his notes were all style corrections. The University of Basel appointed a commission—which included Borrhaus—to look into the alleged misconduct of their colleague. It concluded that Curione's marginal notes were so shocking that they must have been reductio ad absurdum demonstrations, meant to show Gribaldi the tendency of his errant ideas. They did not pursue the matter further.

Curione may have attended an important meeting of Italian Anabaptists, held in Venice in 1550. The conference leader, Peter Manelfi, when later questioned by the Inquisition, named Curione as having been among the participants. In 1553 Curione's enemy, Vergerio, accused him of having been rebaptized. Curione approved of adult baptism, but was critical of the Spiritualist Anabaptists. When the Basel faculty voted to condemn the Anabaptist David Joris in 1559 (posthumously, he had died in 1556), Curione and Castellio were both absent. They both later submitted their disapprobation in writing. Curione's was published as David Joris, Dutch Heresiarch, Life and Doctrine, 1560.

Three of Curione's daughters perished in an epidemic in 1564. His son Orazio (1534-64), an imperial privy councilor and his agent in publishing De amplitudine, also died that year. Orazio possessed a manuscript copy of Servetus's Christianismi Restitutio, 1553, that he may have received from his father. Another son, Agostino (1538-66), like his father a professor of rhetoric at Basel, died soon after. After Curione himself died, his sole remaining son, Leone (1536-1601), composed a short manuscript biography.

Some of Curione's letters can be found in Giuseppe Paladino, Opuscoli e Lettere di Reformatori Italiano del Cinquecento (1927) and in Holt N. Parker, Olympia Morata: The Complete Writings of an Italian Heretic (2003). Among the works by Curione not specifically mentioned above are an edition of Juvenal (1541); On the Immortality of Souls (De immortalitate animorum, 1541 or 1543); Araneus, or on the Providence of God (Araneus, seu de providentia Dei, 1544), On the Whole Art of Discussion and the Essentials of Writing (De omni artificio disserendi atque tractandi summa, 1547); a preface to Gribaldi's The Story of Francesco Spiera (1549); an introduction to and translation of Juan de Valdés's One Hundred and Ten Divine Considerations (1550); a translation of Appian's History of Rome (1554); School, or Perfect Grammar (Scola sive perfecta grammatica) (1555); an edition of Livy (1555); an analysis of Cicero's orations (1556); an edition of Seneca (1557); an edition of the works of the French humanist Guillaume Budé (1557); and History of the Maltese War (1567). Among his religious works that have been translated into English are A Defense of the True and Ancient Authority of Christ's Church, a 16th century rendition by John Philpot appended to The Examinations and Writings of John Philpot (1842), and Letters and Discourses of Celio Curio (1848). The works of "Lyncurius" are Apologia pro Michaeli Serveto, in Calvini Opera, vol. 15 (1876), translated by David Pingree as "The Apologia of Alphonsus Lyncurius," in John Tedeschi, ed., Italian Reformation Studies in Honor of Laelius Socinus (1965); and the preface to Declarationis Jesu Christi Filii Dei, in Ángel Alcalá, ed., Miguel Servet, Obras Completas, vol. 2 (2004).

Curione's story is told in Robert Wallace, Antitrinitarian Biography, vol. 2 (1850); Jules Bonnet, La Famille de Curione (1878) and Vie d'Olympia Morata (1856); Frederic C. Church, The Italian Reformers, 1534-1564 (1932); Earl Morse Wilbur, A History of Unitarianism: Socinianism and Its Antecedents (1945); Markus Kutter, Celio Secondo Curione, Sein Leben und sein Werk (1955); George Huntston Williams, The Radical Reformation (1962); and Salvatore Caponetto, trans. Anne C. Tedeschi and John Tedeschi, The Protestant Reformation in Sixteenth Century Italy (1999). His role in the works of Alphonsus Lyncurius is analyzed in Stanislas Kot, "L'influence de Michel Servet sur le mouvement antitrinitarien en Pologne et en Transylvanie," Bruno Becker, ed., Autour de Michel Servet et Sébastian Castellion (1953) and Uwe Plath, Calvin und Basel in den Jahren 1552-1556 (1974). His collaboration with Castellio is studied in Roland Bainton, trans., Concerning Heretics (1935). De amplitudine is briefly discussed in Robert Burton, Anatomy of Melancholy (1621). The narrator of Edgar Allan Poe's "Berenice" (1835) claims to have studied De amplitudine, "the treatise of the noble Italian, Coelius Secundus Curio."

Article by Peter Hughes