The interaction between dislocations and grain boundaries (GBs) dictates the grain-size dependent strength and ductility in polycrystals. Understanding deformation in the region affected by GB, while explicitly accounting for slip–GB interactions, is therefore important to design microstructures with improved performance. Our study investigates dislocation–GB interactions in a thin bicrystalline strip of 1 micrometer size using a dislocation density-based crystal plasticity (CP) model. The constitutive model tracks Statistically Stored Dislocations (SSDs) and Geometrically Necessary Dislocations (GNDs) at the slip-system level. It explicitly represents dislocation sign and character by including generation and annihilation mechanisms that are consistent with continuum dislocation theory. To capture transport of dislocations, an advection equation is included for dislocation-density evolution. The model is implemented in a Finite Element Method (FEM) framework, where the stress-equilibrium is solved using FEM and the advection equation is solved at each time increment using a finite difference scheme. The model captures the interaction of incoming dislocations with the grain boundary, including piling up, absorption, and transmission of dislocations. The buildup of defects associated with the accumulation of residual dislocations and temporary absorption of the dislocations in the GB region is captured using a GB defect tensor. Since the influence of the GB extends to a finite region around it, the effect of the resistance offered by the GB defects captured using the defect tensor is incorporated through a dynamically evolving resisting energy term that decays exponentially with distance from the GB, thereby influencing the local state in its vicinity. A key capability of the model is that it captures dislocation pile-up and transmission through the GB region simultaneously from either side of the boundary, and quantifies how this complex mechanisms alter the local stress state in the GB region. Simulations are performed under displacement-controlled loading for compression and extension applied perpendicular and parallel to the GB. The effect of misorientation angle as well as the direction and nature of loading is analyzed for all these cases. The response is analyzed through the evolution of dislocation density and resolved shear stress in the GB region, together with the macroscopic stress–strain behavior of the bicrystalline strip.