The heterogeneous evolution of intragranular strain within polycrystalline copper grains is evaluated by in-situ electron back-scattering diffraction during uniaxial tension. Deformation heterogeneity between grains causes a proliferation of slip bands within grains and leads to lattice rotation within grains. The magnitude of intragranular orientation gradient development caused by lattice rotation is dependent on the initial grain orientation as well as grain interactions with its local neighbourhood. Uniaxial tensile deformation is accommodated by the activation of coplanar and non-coplanar slip systems with the highest and second highest Schmid factor values. Non-coplanar slip is predominantly observed in unstable 011 and “Other” (i.e.- those that do not belong to the 111, 001, and 011 fibres) grains. Viscoplastic self-consistent simulations revealed that the interactions with the homologous effective mediums provide additional rotation pathways for unstable 011 and “Other” grains to rotate towards more stable 111 and 001 orientations.