In this study, B4C-TiB2 nanocomposite powder was synthesized from oxide raw materials with the principle of magnesiothermic reduction in B2O3–TiO2–Mg–C system by SHS method. For the SHS process, Mg and C stoichiometries were optimized with thermochemical simulation, and composite charge stoichiometry and Mg particle size were optimized with XRD, BET and SEM analyzes. Optimization of acid concentration, leaching temperature, and leaching time parameters has been provided for the HCl leaching processes carried out to remove undesired by-products after SHS. In addition, pH and temperature changes during leaching were analyzed and an innovative application of modified leaching with H2O2 and carbonic acid addition was investigated. The results showed that by optimizing the process steps for the synthesis of B4C–TiB2 composite nanoparticle by the SHS method, a commercial grade product with a surface area of 30.6 m2/g, and a particle size of 193 nm was obtained.