Targeting to obtain fine dispersions of nanoscale precipitates to enhance the mechanical properties of a highperformance tool steel, re-engineering of the alloy composition and heat treatment was guided by computational thermodynamics and kinetics. A prototype alloy was prepared using the designed chemistry and heat treatment. Thereafter, advanced microstructural characterization and mechanical testing confirmed the successful design to reach a high number density of (V, Mo)C precipitates with an average diameter of about 5 nm in the peak-hardened condition, after tempering the martensite at 600 degrees C for 2 h.