He spent a sabbatical year at Stanford University on an Eleanor Roosevelt Fellowship of the American Cancer Society with Arthur Kornberg (1978–79).

He was the Director of the Cambridge Centre for Protein Engineering from 1990 to 2010 when, on reaching the retirement age, he became an Emeritus Group Leader at the Laboratory of Molecular Biology.

[20] His nomination for the Royal Society reads: Distinguished for work on mechanisms of enzyme catalysis, especially by stopped and quenched flow methods.

He showed that a slow relaxation of chymotrypsin was not a chemical step on the reaction pathway, but a pH-dependent isomerisation between active and inactive forms, and investigated the energetics and equilibria of the transition.

He elucidated the leaving-group specificity, leading to a detailed structural interpretation which showed the energetics of "strain" at the binding site.

He demonstrated that their precise specificity depends on consecutive independent recognition steps, and under appropriate conditions he trapped a transiently discharged aminoacyl tRNA.

Fersht has shown how binding energy can be used to enhance either specificity or rate in an enzymatic reaction, leading to a demonstration of thermodynamic limitations on mechanisms of the "induced fit" type.

He currently works on mutations that affect the stability and activity of the tumour suppressor p53 and how mutants may be "rescued" by small molecule drugs.

His contributions have been widely recognised nationally and internationally by prizes for both chemistry and molecular biology, and by memberships of foreign academies.