In this dissertation, I argue that the second-century bishop Irenaeus of Lyon should be understood within the context of Greco-Roman rhetorical traditions. Irenaeus saw deep continuities between the persuasiveness of the rhetor's word and the persuasiveness of God's Word in the Scriptures, in the person of Christ, and in the apostolic tradition. This rhetorical focus allows Irenaeus to harmonize the Old and New Testaments and the many voices within those testaments. With the study of rhetoric, I examine Irenaeus's theology under five headings: martyrdom, genealogy, apocalypse, prophecy, and eschatology. I then connect these five headings to the five moments in a rhetorical speech: prooimium, narratio, probatio, refutatio, and recapitulatio.