Here we report an electrochemically switchable reversible addition-fragmentation chain transfer polymerization (eRAFT). A new family of biochemical coenzymes are discovered that can be used as highly efficient electroredox catalysts to mediate this polymerization. The oxidation of coenzyme, nicotinamide adenine dinucleotide (NADH), can promote the reduction of a chain transfer agent, triggering generation and propagation of polymer radicals. External potential can activate the reduction of the NAD+ oxidized state and pause the propagation. Tuning the applied potential to reversibly switch the catalyst between its reduced and oxidized states can toggle the polymerization between ON and OFF states. This new strategy is universal to a broad scope of monomers, and ppm-level coenzymes result in the desirable polymer structures with targeted molecular weight, dispersity, and excellent chain-end fidelity. We envisage that the bioorganic-based catalysts would open new directions of organocatalyzed electro-controlled polymerization and be of value in electrocatalysis for well-structured polymers.