Appealing to the testimonies of Justin Martyr in support of a particular view of millennialism can be very tricky. In eschatological debates Justin Martyr is often evoked, and rightly so, in support of historical premillennialism, a view that Christ Jesus will reign for literally a millennium after his second return. Justin, for example in his dialogue with Trypho the Jew, understood the prophesies of Ezekiel and Isaiah and other prophets will be fulfilled at the second coming of Christ Jesus (Just. Dial.c. Tryph. 80, 81).
What is often overlooked is the fact that Justin was far from being consistence in his eschatological views. In his First Apology, the works that does not mention the great tribulation, antichrist or millennium for example, Justin presented a totally different understanding of Old Testament’s prophecies compared to his Dialogue with Tyrpho. The prophecies of Isaiah 2:3 and Psalms 110:2, for instance, are not applied in future millennial reignship of Jesus, as we would expect from his premillenialistic views in Dialogue. Justin understood these prophecies, in realized eschatological and amillennialistic sense, viz., the prophecies has already been fulfilled in the times of Jesus’ disciples and their followers (Just. 1 Apol. 39; 45; 50-52).
Both Dialogue with Trypho and Apologies are attributed to Justin and the inconsistence in his eschatology did not escape the works of L. W. Barnard (1967:157-168) and E. R. Goodenough (1968:281).
So was Justin Martyr a premillennialist or amillennialist? Well, in his Dialogue, he was certainly a premillennialist while in Apologies he was an amillennialist. He was both I will answer. Inconsistent? Yeap.
Barnard, L. W. (1967) Justin Martyr. Cambridge: Cambridge University Press
Goodenough, E. R. (1968) The Theology of Justin Martyr. Amsterdam: Philo Press