Roman Ambitions explores papal politics and humanist culture through the biographical framework of Thomas James (d. 1504), a Breton cleric who spent nearly two decades in Rome. The Italian Wars (1494–98) waged by King Charles VIII are often considered a seminal turning point in the reception of humanist ideals at the French courts, but some historians place Thomas James among the forerunners. Did Thomas James, in fact, influence the transmission of Renaissance culture to parts of France? This study investigates that contention by examining textual, visual, and material sources regarding his identity, activities, and social milieu in Italy and France. Castellan of the Castel Sant’Angelo under Sixtus IV, familiare of the Riario household, and apostolic secretary under Innocent VIII, James had inside knowledge of the Pazzi Conspiracy against the Medici family. Learned in Latin rhetoric from his advanced legal education, he dined with prominent humanists, including Giulio Pomponio Leto, founder of the Accademia romana. James was an important eyewitness, an adaptive and pragmatic passenger between cultures, whose life offers a lens through which to observe Church politics and cultural transmission in early modern Europe. The monograph’s subject and themes will appeal to an audience of academics, scholars, and advanced postgraduate students in the humanities, particularly historians in late medieval and Renaissance studies.