Three full-scale retrofitted unreinforced masonry (URM) walls and an unstrengthened URM wall were tested under constant axial load and cyclic lateral loads in order to evaluate the effect of a strengthening procedure developed using unbonded prestressed wire rope units on enhancing the in-plane shear strength and ductility of unreinforced concrete brick masonry walls. The spacing of wire ropes varied between 150 mm and 450 mm at the constant wall aspect ratio of 0.85. The ductility of the walls tested was evaluated using the work damage indicator, suggested by Sheikh and Khoury, calculated at each loading step from the hysteretic loops. The in-plane shear strength of walls tested was also compared with predictions obtained from the simple equations proposed to identify the shear transfer capacities of masonry and wire ropes. Test results showed that the developed strengthening procedure was highly effective in enhancing the shear cracking strength, ultimate shear strength and ductility of URM walls and controlling crack propagation along head and bed mortar joints. Higher shear strength and work damage indicator were observed in the retrofitted URM walls than in unstrengthened URM wall by 2.85 and 3.48 times, respectively, for $s_w$ of 150 mm, by 2.41 and 3.08 times, respectively, for $s_w$ of 300 mm and by 2.05 and 2.14 times, respectively, for $s_w$ of 450 mm, where $s_w$ is the spacing of inclined wire ropes. The shear capacities predicted from the proposed simple equations were in good agreement with test results.