Enantioselective hydrogen atom transfer (HAT) has great synthetic potential, but the de novo design of chiral HAT catalysts is challenging. We report a conceptually distinct approach in which chiral HAT catalysts are generated in situ through non-covalent self-assembly of privileged chiral phosphoric acids and commercial 2-mercaptopyridines. The phosphoric acid serves as a modular chiral source that renders the achiral thiol effectively chiral, enabling a previously inaccessible combinatorial space of chiral HAT catalysts. This platform enabled the photochemical deracemization of 2-aryl pyrrolidines, a prevalent scaffold in active pharmaceutical ingredients. Optical enrichment proceeds via enantioselective hydrogen atom relay, in which a single chiral assembly orchestrates both hydrogen atom abstraction and delivery. This concept of relaying chiral information via non-covalent assembly holds broad potential for asymmetric radical catalysis.