Herein, we introduce a bottom-up material design approach of optically selective SiC-based nanocomposite objects. Precursors have been firstly synthesized by reaction of allylhydridopolycarbosilane with titanium and boron complexes before a pyrolysis at 1000 °C in flowing argon to deliver single-phase amorphous Si–Ti–C–N(B,H) ceramics. The later was then heat-treated up to 1800 °C under argon. Relatively dense nanocomposites made of TiCxN1-x (0 ≤ x ≤ 1) nanocrystals homogeneously formed in situ in a SiCxN4-x-type phases (0 ≤ x ≤ 4) have been isolated after heat-treatment at 1400 °C. Above 1400 °C, our experimental data showed a continuous evolution of carbon and nitrogen contents up to 1800 °C due to carbothermal reduction reactions forming carbide phases while releasing nitrogen-containing species. Thus, heat-treatment at 1800 °C led to porous and fully crystallized TiC(N)/SiC(B) nanocomposites that displayed a maximal optical selectivity of 1.67 measured at room temperature; a value significantly increased compared to the SiC(B) counterpart.