Abstract: In response to the gap between existing research on undamaged reinforced concrete (RC) beams and the practical need for strengthening damaged structures, this study investigates the use of High-strength stainless steel wire mesh reinforced engineered cementitious composite (HSSWM/ECC) to strengthen pre-damaged RC beams in shear. Tests were conducted on eight beams considering varying damage levels, reinforcement ratios, and strengthening configurations. The results show that the strengthened beams failed in shear-compression mode with multiple cracking in the HSSWM/ECC, which improved ductility. Compared to unstrengthened beams, the strengthened ones exhibited increases of 23–48% in shear capacity, 25–83% in ultimate deflection, 30–195% in toughness, and 10–33% in ductility. However, higher initial damage led to exponential growth in residual strains in stirrups and concrete, accelerating strain development in the strengthening layer and reducing its effectiveness. Increasing the reinforcement ratio or using fully-wrapped cast-in-situ and both-sided bonding configurations further enhanced shear performance. A new shear capacity model based on the modified compression field theory and incorporating residual strain effects was developed. The proposed model shows higher accuracy and applicability compared to existing models, providing a reliable basis for the design of strengthened RC structures.