<p>This study investigates the influence of martensitic start temperature on residual stress and distortion. A double-sided fully welded T-joint was fabricated by welding a high-alloy base material (1.4318) with two different filler wire combinations (G19 9, G4Si1). The temperature distribution and distortion were measured during the welding process using thermocouples and displacement transducers. The thermo-metallurgical-mechanical effect was considered when computing a numerical simulation model for a T-joint geometry. A phase transformation model was incorporated to predict martensite formation during welding, with the martensite start temperature varied as a parameter. Further, the mechanical model was developed by integrating the thermal strains, phase strains, and mechanical strains. Results from numerical simulations and experimental measurements are compared and analyzed to assess the impact of martensite start temperature on residual stresses and distortion. From the findings, it was found that, at a reduced martensitic start temperature, there was a significant reduction in residual stresses and distortion.</p>