More than half of the solar spectrum is near infrared (NIR) light, which is seldom utilized in photocatalytic reactions. In this work, an Ag–g-C₃N₄/W₁₈O₄₉ heterojunction catalyst is prepared and used for full-spectrum-driven N₂ photofixation from the UV to the NIR region for the first time. X-ray diffraction, N₂ adsorption, UV-Vis-NIR spectroscopy, thermogravimetric analysis, photoluminescence, X-ray photoelectron spectroscopy and electrochemical impedance spectra were used to characterize the prepared catalysts. The result indicates that the as-prepared Ag–g-C₃N₄/W₁₈O₄₉ heterojunction catalysts display much higher N₂ photofixation performance than that of individual W₁₈O₄₉ or Ag–g-C₃N₄, which should be due to the better separation rate of electron–hole pairs and more efficient light utilization. g-C₃N₄ is the active component in the catalyst for N₂ photofixation. Ag loading promotes the separation rate of electron–hole pairs. W₁₈O₄₉ plays a role as light absorber in the full-spectrum to form more photogenerated electrons for recombining the holes in the g-C₃N₄ through “Z-scheme” mechanism. A possible electrons transfer route is proposed.