Anthony Kirby has conducted fundamental quantitative studies on the chemical mechanisms involved in catalysis by enzymes. His approach has been to mimic the way substrate and catalytic groups interact in the enzyme–substrate complex by bringing together the same functional groups in various ways in systems which are simple enough to understand in detail.

He has investigated reactions of all the major substrate groups. His work on phosphate monoesters laid the foundation of our current understanding of the phosphate transfer process, the most common enzyme-catalysed reaction, and has recently been extended to the basic reactions of diesters and triesters.

His studies on amides have produced the most efficient known intramolecular reaction, rivalling some enzymes in efficiency and resembling them mechanistically. This led to the establishment of predictive generalisations which he has used to develop the best defined and most efficient bifunctional models for enzyme reactions currently available. His important work on acetals has far-reaching implications, not only for the mechanisms of glycosidic enzymes, but also for the basic chemistry of related oxygen compounds.