The study aims to explore the microstructure and mechanical characteristics of the gas tungsten arc welded joint in heat-resistant P92 steel under varying heat-treatment conditions. The welded joint undergoes tempering at 760 °C for 90 min, employing different cooling methods such as air cooling, furnace cooling, and water quenching. The welded joint were examined utilizing field emission scanning electron microscopy (FE-SEM) and optical microscopy. To assess the impact of heat treatment on mechanical properties, room-temperature and high-temperature tensile testing, microhardness testing, and Charpy impact toughness testing was performed. The fractured tensile and impact tested specimen was subjected to SEM characterization to investigate the fracture mode and failure mechanism. Among different heat-treatment conditions, the tempering process at 760 °C/90 min with air cooling exhibited the optimal combination, showcasing a tensile strength of 631 MPa, hardness of 284 ± 5 HV, and Charpy impact toughness of 142 ± 7.5 J.