Synthetic polymers have become indispensable to modern society. The development of living and controlled polymerization methodologies have enabled the synthesis of precise macromolecular architectures with tailored polymer properties for integration in diverse applications. This presentation will discuss the design and synthesis of strongly reducing visible-light organic photoredox catalysts for organocatalyzed atom transfer radical polymerization. Developing catalyst design principles and their implications in the polymerization mechanism to synthesize well-defined macromolecules will be presented.