Boron carbide (B4C) is widely used in nuclear reactors, wear-resistant components, abrasive materials, and lightweight armors because of its outstanding properties such as high melting point, low density, high hardness, high neutron absorption capability, and good wear resistance. However, high temperatures and long sintering times are required to obtain dense structures via conventional pressure-assisted sintering methods and it has low fracture toughness which limits its applications. Therefore, addition of an appropriate second phase and novel methods such as spark plasma sintering (SPS) emerges in the latest studies to overcome the limitations of B4C. Zirconium diboride (ZrB2) is a candidate material to promote boron carbide’s consolidation and achieve good mechanical properties. In this study, B4C-ZrB2 composites in square geometry with varying amounts of ZrB2 (0–15 vol. %) were prepared by SPS. The effects of ZrB2 addition on the densification, hardness, and fracture toughness were investigated.