There is a lack of knowledge regarding the parameters needed for the effective seismic performance assessment of historical stone masonry buildings. The paper presents the results of an extensive experimental campaign consisting of four compression and fifteen in-plane cyclic shear tests on three-leaf ashlar stone masonry walls and its constituents. The morphology, level of vertical load, and testing boundary conditions were systematically varied, and their influence on the load-bearing and deformation capacities, stiffness, ductility and energy dissipation was analysed. Good consolidation of the inner core enables in-plane failure mechanism of the walls to occur without decisive out-of-plane damage. The boundary conditions applied significantly influence the failure modes and large deformation capacities obtained, whereas transverse connections in the case of a shear failure mechanism do not significantly influence the overall lateral in-plane response of walls.