TiB2/2024 aluminum matrix composites were prepared in situ from the Al–K2TiF6–KBF4 reaction system; then, we investigated the microstructure and mechanical properties of the composites in the as-cast and extruded states. X-ray diffraction (XRD) and scanning electronic microscope (SEM) analyses showed that TiB2 particles were successfully produced in the matrix by the in situ reactions. The optimal content of TiB2 particles in the composites was 3 wt.%; moreover, the size of α-Al grains in the microstructure of the composites with 3 wt.% content was the smallest among the composites reinforced with different content of TiB2 particles, and the TiB2 particles showed a uniform distribution. The tensile strength and elongation of the composites (246 MPa and 9.8%, respectively) were 21.8% and 18.1% higher compared with those of the alloy matrix. When the TiB2 particle content was 5 wt.%, the cast composite exhibited the highest hardness of 113 HBW, which was 43.0% higher than that of the base alloy. Fracture analysis showed that the fracture mode changed from ductile to brittle as the mass fraction of TiB2in the composite increased. The mechanical properties of the 3 wt.% TiB2/2024 aluminum matrix composite were significantly improved after hot extrusion, with tensile strength and elongation values of 375 MPa and 19.7%, respectively, which were 52.4% and 101% higher than those of the as-cast material.