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The present study deals with the development of α-SiAlON-4%Co and α-SiAlON-20%TiCN ceramic composites with desirable properties tailored for enhanced high-cutting tool performance. The effective medium theories and mean-field homogenization schemes are used to design and optimize the volume fractions, the interfacial thermal resistance, and reinforcement particle sizes while incorporating the influence of porosity on the effective properties of the ceramic composites. The designed composites are fabricated via the spark plasma sintering process. The ceramic samples are characterized/analyzed via scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The effective thermal and structural properties of the composites are measured and compared to that of the computational predictions. The results indicate that excellent densification in α-SiAlON-based composites can be achieved by the use of spark plasma sintering process. Experimentally measured properties of SiAlON-20%TiCN composite compare well with that of the computational predictions and have shown significant enhancement in its effective thermal conductivity and fracture toughness. The measured properties of SiAlON-4%Co composite did not meet the predictions due to Co agglomeration and the large thermal mismatch between the matrix and the inclusion, which emphasizes the need to optimize the synthesis process and establish volume fraction limits of Co in α-SiAlON ceramic composites.