High-entropy carbide (HEC) ceramics exhibit exceptional potential surpassing that of conventional ceramics in terms of hardness, thermal stability, irradiation resistance, and oxidation resistance, thereby holding broad application prospects. Nevertheless, their intrinsic brittleness remains a critical bottleneck constraining engineering application. In this study, nano-SiC (n-SiC) was employed as a reinforcing phase to fabricate HEC-n-SiC composite ceramics via high-pressure high-temperature (HPHT) sintering. The results demonstrate that under the optimal sintering conditions of 5 GPa, 2000 ℃, and a holding time of 15 min, the specimens achieve the highest relative density and the finest grain size (135.6 nm). SiC is successfully dissolved into the high-entropy carbide lattice, forming a six-component solid solution. At an HEC:SiC molar ratio of 9:1, the material exhibits optimum comprehensive performance, with a hardness of 24.0 GPa and a fracture toughness of 10.2 MPa·m^1/2, achieving a synergistic enhancement of hardness and toughness. Crack morphology observations and TEM characterization reveal that the strengthening and toughening mechanisms predominantly include: n-SiC-induced lattice distortion giving rise to dislocations and stacking faults, which contribute to solid-solution strengthening, while simultaneously promoting crack deflection that dissipates additional fracture energy and thereby enhances toughness. This work extends the second-phase strengthening strategy from conventional “interfacial toughening” to “intra-lattice toughening”, providing a novel paradigm for the design and fabrication of high-performance high-entropy ceramics.