We report the large-scale synthesis of porous graphitic carbon nitride (g-C3N4) in a direct heat treatment process by controlling the thermal condensation temperature of the low-cost urea precursor. An excellent linear relation between the yield of the urea-derived porous g-C3N4 (U-g-C3N4) and the input urea was experimentally demonstrated, and consequently, a large-scale yield >50 g in a batch was readily achieved. A series of morphology and structure characterizations revealed the actual evolutionary process of the temperature-dependent porous architecture of U-g-C3N4 and its inherent superiority. Furthermore, we demonstrated the extraordinary visible-light-driven photodegradation activity of large-scale U-g-C3N4 toward organic pollutants such as rhodamine B, safranine T, and alpha-naphthol. Such superior photodegradation performance and long-term photocatalytic stability, together with a scalable preparation method, may render as-fabricated U-g-C3N4 as a promising candidate for practical application in environmental remediation.