The present study investigates the influence of heat input on microstructure evolution and mechanical properties of nitronic steel and super duplex stainless steel dissimilar welded joints. For this experimental purpose, carbon steel filler (ER70S–2) was employed using gas tungsten arc welding (GTAW) with two heat input conditions: lower (0.624 kJ/mm) and higher (1.01 kJ/mm). The welded joint was subjected to the microstructure of different zones, including weld metal, base metals, and heat-affected zones/interfaces were accomplished by optical microscopy, scanning electron microscope. Tensile test, Impact test, and Vickers microhardness were conducted to study the mechanical properties. Microstructural evolution in the weld metal and heat-affected zone reported the presence of Type II boundary and macrosegregation. Hardness test investigation reveals that the weld metal’s hardness rises compared to the base metals. Moreover, the weldment hardness decreases at higher heat input than lower heat input. The tensile test study reveals that the lower heat input weldment exhibits more elongation and tensile strength than the higher heat input weldment. The Charpy impact tests show that the average toughness value increases with heat input. The results also indicate that the lower and higher heat input specimen exhibited brittle fracture. © 2022 Taylor & Francis.