A conductive TiC nanopowder was incorporated into nanosized β-Si3N4-based powder and consolidated by a spark plasma sintering (SPS) technique with a rapid heating process. The influence of the conductive phase on the microstructure development of the Si3N4 matrix was demonstrated. After sintering, the conductive phase transformed into titanium oxycarbonitride. The Si3N4-based composite containing 5 wt% nano-TiCxOyNz shows a larger average grain size and aspect ratio than the monolithic Si3N4-based ceramic. This is possibly because a leakage current hops across the conductive titanium oxycarbonitride grains and causes Joule heating during sintering. The transmission electron microscopy analysis confirmed that dissolution–reprecipitation and coalescence occur. In addition, although the increasing amount of incorporated nano-TiCxOyNz (10 and 20 wt%) decreases the electrical resistivity of the composites, the pinning effect of the titanium-based phase significantly suppresses the grain growth of Si3N4 matrix grains. β-Si3N4-based nanocomposites containing nanosized titanium oxycarbonitride were thus obtained in the present study.