Nicotinamide adenine dinucleotide (NAD(+)) is a key redox compound in all living cells responsible for energy transduction, genomic integrity, life-span extension, and neuromodulation. Here, we report a new function of NAD(+) as a molecular photocatalyst in addition to the biological roles. Our spectroscopic and electrochemical analyses reveal light absorption and electronic properties of two pi-conjugated systems of NAD(+). Furthermore, NAD(+) exhibits a robust photostability under UV-Vis-NIR irradiation. We demonstrate photocatalytic redox reactions driven by NAD(+), such as O-2 reduction, H2O oxidation, and the formation of metallic nanoparticles. Beyond the traditional role of NAD(+) as a cofactor in redox biocatalysis, NAD(+) executes direct photoactivation of oxidoreductases through the reduction of enzyme prosthetic groups. Consequently, the synergetic integration of biocatalysis and photocatalysis using NAD(+) enables solar-to-chemical conversion with the highest-ever-recorded turnover frequency and total turnover number of 1263.4 hour(-1) and 1692.3, respectively, for light-driven biocatalytic trans-hydrogenation.