The aim of this paper is to investigate the effects of microstructural parameters such as the volume fraction, morphology and spatial distribution of the martensite phase and the grain size of the ferrite phase on the plasticity and localized deformation of dual-phase (DP) steels. For this purpose, Voronoi based representative volume elements (RVEs) are subjected to proportional loading with constant stress triaxility. Two alternative approaches are employed in a comparative way to model the plastic response of the ferrite phase, namely, micromechanically motivated crystal plasticity and phenomenological J2 flow theory. The plastic response of the martensite phase, however, is modeled by the J2 flow theory in all the calculations. The predictions of both approaches closely agree with each other in terms of the overall macroscopic response of the DP steels, while clear differences are observed in the localized deformation patterns. The results of the present study are also compared with experimental and computational findings from the literature.