Nanocrystalline gallium nitride powder was synthesized from a gallium dimethylamide-derived polymeric precursor by pyrolysis in ammonia atmosphere to study the grain growth mechanisms in the temperature range 800–1150 °C. In particular, growth exponents and activation energies were determined. Up to 900 °C, grain growth was inhibited, whereas, above 1000 °C, evaporation–condensation was identified as the dominant material transport path.