This study investigates the influence of adding a cold wire during gas metal arc welding (CW-GMAW) for repair of S275JR structural steel. The research is aimed at improving repair productivity through increased deposition rates with enhanced performance. During weld repair, multiple passes induce large number of thermal cycles and a huge thermal gradient on the material which has an adverse effect on the material’s properties. This is largely due to the microstructuralMicrostructural changes that occur during the process. In this work, a systematic approach has been adopted to explore the effects of varying gas metal arc welding (GMAW) parameters, including wire feed rate, welding currentWelding current, voltage, travel speed, and specifically cold-wire feed speed on the heat affected zone (HAZ) microstructureMicrostructure and hardnessHardness. Macrostructural examination highlights significant alterations in the heat affected zone (HAZ) region, with marked microhardnessMicrohardness changes in both WM and HAZ. Cold-wire addition led to a reduction in the HAZ area, depth of weld metal penetration, and significantly reduced the impact of imposing thermal cycles on the HAZ of the welded samples. Additionally, microstructuralMicrostructural analysis was conducted using a standard optical microscope to correlate the observed hardnessHardness variations with microstructuralMicrostructural transformations in the weld metal and heat affected zone (HAZ). The findings reveal that specific combinations of CW-GMAW parameters can significantly influence the microstructureMicrostructure and thereby hardnessHardness, suggesting that with careful control of these parameters, it would be possible to do faster repair with minimal lossCold-wire Gas Metal Arc Welding (CW-GMAW) of integrity for critical structural steels.