A mesoscale model for modeling a geopolymer concrete (GPC) in tension and compression using the Drucker–Prager yield criterion for the GPC in compression and Rankin’s criterion in tension is proposed. The von Mises isotropic plasticity model with a negative hardening modulus is used for modeling the short-steel-fiber pull-out behavior. A computationally efficient fiber generator that takes into account the specific fiber orientation near surfaces is developed. An uncoupled upscaling method of mesoscale simulation is proposed for an efficient and accurate modeling of macroscale structural elements. Results showed that the numerical models proposed exhibited a good agreement with experimental measurements in tensile, compression, and flexural tests. The numerical models can be used to estimate the load-bearing capacity of structural elements, such as beams, where short fibers and a macroscopic reinforcement are mixed in a GPC matrix.