one of the most important of the Greek philosopher-Apologists in the early Christian church. His writings represent the first positive encounter of Christian revelation with Greek philosophy and laid the basis for a theology of history.

A pagan reared in a Jewish environment, Justin studied Stoic, Platonic, and other pagan philosophies and then became a Christian in 132, possibly at Ephesus, near modern Selçuk, Turkey. Soon after 135 he began wandering from place to place proclaiming his newfound Christian philosophy in the hope of converting educated pagans to it. He spent a considerable time in Rome. Some years later, after debating with the cynic Crescens, Justin was denounced to the Roman prefect as subversive and condemned to death. Authentic records of his martyrdom survive.

Of the works bearing Justin's authorship and still deemed genuine are two Apologies and the Dialogue with Trypho. The first, or “Major Apology,” was addressed about 150 to the Roman emperors Antoninus Pius and Marcus Aurelius. In the first part of the First Apology, Justin defends his fellow Christians against the charges of atheism and hostility to the Roman state. He then goes on to express the core of his Christian philosophy: the highest aspiration of both Christianity and Platonic philosophy (Platonism) is a transcendent and unchangeable God; consequently, an intellectual articulation of the Christian faith would demonstrate its harmony with reason. Such a convergence is rooted in the relationship between human reason and the divine mind, both identified by the same term, logos (Greek: “intellect,” “word”), which enables man to understand basic truths regarding the world, time, creation, freedom, the human soul's affinity with the divine spirit, and the recognition of good and evil.

Justin asserts that Jesus Christ is the incarnation of the entire divine logos and thus of these basic truths, whereas only traces of truth were found in the great works of the pagan philosophers. The purpose of Christ's coming into the world was to teach men the truth and save them from the power of demons. In the third part of the First Apology, Justin vividly describes the early Christians' method of celebrating the Eucharist and of administering Baptism.

The Dialogue with Trypho is a discussion in which Justin tries to prove the truth of Christianity to a learned Jew named Trypho. Justin attempts to demonstrate that a new convenant has superseded the old covenant of God with the Jewish people; that Jesus is both the messiah announced by the Old Testament prophets and the preexisting logos through whom God revealed himself in the Scriptures; and that the gentiles have been chosen to replace Israel as God's chosen people. In his brief Second Apology Justin argues that the Christians are being unjustly persecuted by Rome.

Justin's distinctive contribution to Christian theology is his conception of a divine plan in history, a process of salvation structured by God, wherein the various historical epochs have been integrated into an organic unity directed toward a supernatural end; the Old Testament and Greek philosophy met to form the single stream of Christianity.

Justin's concrete description of the sacramental celebrations of Baptism and the Eucharist remain a principal source for the history of the primitive church. Justin serves, moreover, as a crucial witness to the status of the 2nd-century New Testament corpus, mentioning the first three Gospels and quoting and paraphrasing the letters of Paul and 1 Peter; he was the first known writer to quote from the Acts of the Apostles.