<p>Carbon dots (CDs) have shown great potential as photocatalysts for photoinduced atom transfer radical polymerization (photo-ATRP), offering high polymerization rates and precise control over polymer structures. However, their reliance on high-energy ultraviolet (UV) or blue light causes side reactions and restricts practical application. To overcome this limitation, we developed red-light-active pyridine nitrogen-doped CDs through an HNO₃-assisted hydrothermal method. The optimized material, nCD-50, exhibited strong absorption in the red region and outstanding photocatalytic activity under 640 nm light, enabling the synthesis of well-defined polymers with predictable molecular weights and low dispersity. The system was responsive to both light and pH switching. Under red light, the polymerization rates showed strong pH-dependence: it was more than two times faster under acidic conditions than under neutral pH, and nearly ceased in alkaline environments. In contrast, blue light irradiation resulted in fast polymerization without observable pH dependence, achieving near-quantitative monomer conversion within 1 h. This performance exceeds most reported CDs-based photocatalysts. Moreover, the nCD-50-based system enabled scalable polymer production in a continuous flow reactor. This work provides a strategic design for efficient long-wavelength photocatalysts and advances the potential of photo-ATRP for industrial applications.</p>