Justin Martyr (ca. 114-ca. 165 A.D.) is without a doubt the most important of the Greek apologists of the 2nd century. Born into a Greek and pagan family in the Palestinian town of Shechem, Justin was befriended by a wise elderly Christian who showed him the truth of the Old Testament Scriptures fulfilled in Christ. Previously, Justin had explored almost every possible philosophical school then in existence, including Stoicism, Aristotelianism, Platonism and the school of Pythagoras. However, he found in the witness of this elderly Christian a "flame kindled in my soul; and a love of the prophets, and of those men who are friends of Christ... I found this philosophy alone to be safe and profitable" (Dialogue 8.1).

Because his writings are permeated with the idea of the seminal Logos, and because he mentions his own philosophical background in his writings, the philosophical aspect of his writings is sometimes over-emphasized. Although he remained a philosopher instead of becoming a priest or bishop, Justin's faith was not just a philosophy. He believed that Christianity was the true philosophy—a philosophy he was willing to defend and for which he was willing to die. The apologies he composed and delivered to the Emperor and Senate did not apologize for being Christian. They defended Christianity, which is what apologia means in Greek. He confronted the Roman judicial system of his day, demonstrating the injustice of condemning Christians simply because they bear the name.

In Justin's time, caricatures of Christianity were common, and these caricatures enabled people to more easily persecute Christians. In his first Apology, Justin explains in simple terms what it means to be a Christian. He describes the Christian as the best kind of citizen, in contrast to the pagan lifestyle of Rome's dominant citizenry. As an added benefit of his defense of the Christian lifestyle, we gain one of the earliest descriptions of what Christian baptism and its Eucharistic worship life must have looked like in the first half of the second century (Apology 61, 65-67). In Justin's second Apology, this time addressed to the Roman Senate, he continues to address the lack of diversity in a Roman society which refuses to tolerate Christianity. He compares the persecution of Christians to that of Socrates who was also killed for speaking the truth (Apology 2.10).

Composed after his two Apologies, Justin put into writing his famous Dialogue with Trypho, where he amicably presented this highly regarded Jewish rabbi (d. 134 A.D.) with a Christocentric interpretation of the Old Testament and the implications of this for the New Israel that was now on the scene. Trypho himself was favorably impressed, indicating a desire to dialog more frequently (Dialogue 142). Despite this amicable interchange, not everyone responded positively to Justin's passionate defense of Christianity. Perhaps at the instigation of the rival Cynic philosophers, Justin was brought up on charges of atheism—a not uncommon charge of the day because the Romans held their pantheon of gods in high regard. Justin and six other Christians appeared before the prefect of the Senate, Junius Rusticus. After boldly confessing their faith, they refused to offer incense to the gods of Rome. Rusticus ordered them to be scourged and then beheaded. The date of his martyrdom is given as around the year 165 A.D. during the reign of Marcus Aurelius.