Abstract: Several high-throughput optical screening methods for the photocatalytic activity of a structurally diverse library of cationic iridium (III) complexes ([Ir(C^N)₂N^N)]⁺), where C^N is a cyclometalating ligand and N^N an ancillary ligand, were developed. These low-cost colorimetric assays allow for real-time monitoring of photo-induced electron transfer processes involved in hydrogen evolution and organic photoredox reactions. The infrastructure we have built is useful for generating large standardized experimental datasets. The obtained rate constants of the [Ir(C^N)₂N^N)]⁺ photocatalysts are then correlated to calculated chemical descriptors such as density functional theory (DFT)-derived features to help establish structure-activity relationships. This data-driven approach to chemical research is necessary to accelerate discovery of faster and chemo-selective catalysts.