We present in this paper a micromechanics-based elasto-viscoplastic approach for modeling the time-dependent deformation of granite. Inspired by the polycrystalline theory of metallic materials, the sliding behavior in an individual grain is regarded as the sole source of plastic deformation, which is characterized by a Mohr–Coulomb-type yield criterion and a non-associated plastic potential. The micro–macro transition is realized within the framework of Hill's self-consistent approach. The performance of the proposed model is evaluated by several case studies and by reproducing experimental data.