Ni–Mo alloy claddings were fabricated on low-carbon steel substrates using powder metallurgy combined with hot isostatic pressing (PM-HIP). The interfacial microstructure, elemental interdiffusion, phase composition and microhardness distribution of the bimetallic composite were investigated systematically. The results show that sound metallurgical bonding without pores, cracks and element dilution is achieved under the HIP process of 1100 °C, 120 MPa and 4 h holding time. Interdiffusion of Fe, Ni and Mo atoms forms a 20–50 μm thick interfacial transition layer, and Mo exhibits a relatively low diffusion capacity due to its large atomic radius. Two intermetallic phases, Ni₄Mo and NiMo, are formed in the cladding layer because of the inhomogeneous distribution of Mo. A prominent microhardness gradient is observed throughout the composite, and the interfacial layer presents the highest hardness of 905 HV resulting from multiple strengthening mechanisms. As an effective alternative to traditional welding and cladding technologies, the PM-HIP process exhibits great potential for manufacturing complex bimetallic components with prospective service prospects in severe corrosive environments.