This contribution reports, for the first time, the sintering, microstructure and properties of in situ synthesized/consolidated eutectic composites by spark-plasma sintering (SPS). SPS involves a number of processing parameters that may be used to tailor the composition of eutectic composites. It was shown that pressure may be used as a means of controlling the eutectic formation. By changing the pressure, temperature and composition, we propose a processing route that results in the in situ formation of strengthened eutectic composites, consisting of a matrix (B4C, and B4C-NbB2 composite) and also containing regularly distributed whiskers of NbB2. The composites with the eutectic composition of 35 mol.% NbB2 obtained by SPS exhibit a high Vickers hardness (26-27 GPa) and indentation fracture toughness (similar to 6 MPa.m(1/2)).