Irenaeus admired Justin Martyr and borrowed from his writings (AH 4.6.2, 5.26.2) but he could hardly deny to the heretics the right to distinguish between two gods and then approve of Justin's saying that there are two gods. [Denis Minns, Irenaeus: An Introduction p. 60]
But then we have to ask - why do we assume that the Marcionites (i.e. the one's whom Irenaeus and Tertullian spend the most time condemning for 'holding there are two gods') had the same system as Justin? Why couldn't Justin - i.e. the real Justin of history rather than the Church Father whose works were altered by Irenaeus - have been a Marcionite or a sect closely aligned with Marcion?