A doctrine of clemency is reconstructed from Seneca’s “On Clemency,” which is now largely lost. Initially, the Stoic theory of virtues and emotions is explored. Next, we consider Seneca’s doctrine of clemency. He describes clemency through five characteristics: temperance, leniency, inclination to leniency, moderation, and pullback from seemingly merited punishment. First, we compare Seneca and Chrysippus’ contrary descriptions of clemency. Seneca defines clemency as an honorable deed because it resists the vicious tendency to revenge by exercising the virtues of temperance, moderation, and leniency. In contrast, Chrysippus defines clemency as being defective because it fails to inflict an appropriate punishment as determined by law. Second, after recognizing Seneca’s transformation of clemency, we examine his use of Aristotelian tradition. Braund’s philological survey showed the correspondence between the Latin term clementia (clemency) and the Greek term ἐπιείκεια (equity). Seneca’s description contains further Aristotelian ideas, such as magnanimity. Given Seneca’s knowledge of the Peripatetic school, the resemblance of Seneca’s description of clemency to Aristotelian equity is deliberate. These Aristotelian ideas are utilized to erase the early Stoics’ negative stigma of clemency. Thus, Seneca transforms clemency by synthesizing Stoic and Aristotelian virtues.