To understand the underlying mechanisms that control the mechanical properties of nanostructured metals, an insight into the role of the grain boundary in dislocation-driven plastic deformation is vital. The grain boundary has been observed as a dislocation source, sink, or having no effect, which in turn, gives rise to different macroscopic mechanical responses. With this motivation, atomistic simulations and three-dimensional dislocation dynamics simulations were performed to investigate dislocation interactions at various grain boundaries and their role in the plastic deformation of face-centered cubic (FCC) bicrystalline micropillars. The atomistically-informed dislocation dynamics simulations show that bicrystalline samples containing a high angle grain boundary (HAGB) display hardening and higher flow stresses compared to single crystals, while micropillars with a coherent twin boundary (CTB) show similar flow stresses to the reference single crystalline samples. This is due to the transparency of the grain boundary to slip transmission, which is observed in the atomistic simulations. Interestingly, allowing dislocation glide on the grain boundary exhibits a decrease in flow stress as slip transmission becomes easier.