An incrementally nonlinear constitutive relation is formulated to describe the mechanical behaviour of infilled rock joints. This relation is calibrated using a discrete element model, which is validated by experimental data. Since the phenomenological relation fully combines the normal and tangential directions of a rock joint, it can reproduce rock joint features as the dilatancy process and the contribution of compression on tangential stress. To take into account the hardening of the material, the influence of the previous shear loading history on the mechanical response of the rock joint is considered. Finally, the performance of the constitutive relation is verified by showing the good agreement between the responses predicted by the relation and those obtained by the discrete model for different loading paths.