Titanium nitride (TiN) decorated N-doped titania (N-TiO₂) composite (TiN/N-TiO₂) is fabricated via an in situ nitridation using a hydrothermally synthesized TiO₂ and melamine (MA) as raw materials. After the optimization of the reaction condition, the resultant TiN/N-TiO₂ composite delivers a hydrogen evolution activity of up to 703 μmol/h under the full spectrum irradiation of Xe-lamp, which is approximately 2.6 and 32.0 times more than that of TiO₂ and TiN alone, respectively. To explore the underlying photocatalytic mechanism, the crystal phase, morphology, light absorption, energy band structure, element composition, and electrochemical behavior of the composite material are characterized and analyzed. The results indicate that the superior activity is mainly caused by the in situ formation of plasmonic TiN and N-TiO₂ with intimate interface contact, which not only extends the spectral response range, but also accelerates the transfer and separation of the photoexcited hot charge carrier of TiN. The present study provides a fascinating approach to in situ forming nonmetallic plasmonic material/N-doped TiO₂ composite photocatalysts for high-efficiency water splitting.