Maraging steel (MS1)-tool steel (P20) bimetals additively manufactured using the laser powder bed fusion technique were studied under different heat treatment cycles and loading conditions. The hardening of P20 and aging of MS1 were performed sequentially on the hybrid samples. The interfacial characteristics and microstructural evolution of the bulk materials were studied using various advanced electron microscopy techniques. The post-processing procedures successfully produced a uniform martensitic structure throughout the MS1-P20 hybrid steels, leading to a less detectable interface under electron backscatter diffraction (EBSD) imaging. The mechanical performance of heat-treated hybrid steels was evaluated using complex loading conditions. 3-point and 4-point bending tests were performed to assess the impact of heat treatments on the mechanical performance of the hybrid steels. The heat-treated samples exhibited higher strength with relatively homogeneous hardness variations and deformed more uniformly in bending conditions.