Biocatalysis is widely renowned for its remarkable efficiency, selectivity, and known for operating under mild conditions. While most enzymatic reactions progress without light irradiation , recent studies have identified light as a crucial factor in the activation of certain naturally occurring enzymes. These findings have spurred the rapid advancement of photoenzymatic catalysis in the past few years, where enzymes are not typically known for light activation perform excited-state chemistry with or without the presence of external photocatalysts to facilitate new-to-nature transformations that are challenging for traditional chemical synthesis. In this review, we summarize the experimental and computational methods used to investigate the catalytic mechanisms of repurposed photoenzymes with new-to-nature reactivity and discuss how these insights can inform the design of new photoenzymatic catalytic systems.