In 1924 Ingold moved to the University of Leeds where he spent six years as Professor of Organic Chemistry working alongside his wife, Dr. Dr. Edith Hilda Ingold (Usherwood) . He returned to London in 1930, and served for 24 years as head of the chemistry department at University College London, from 1937 until his retirement in 1961.
During his study of alkyl halides, Ingold found evidence for two possible reaction mechanisms for nucleophilic substitution reactions. He found that tertiary alkyl halides underwent a two-step mechanism (S1) while primary and secondary alkyl halides underwent a one-step mechanism (S2). This conclusion was based on the finding that reactions of tertiary alkyl halides with nucleophiles were dependent on the concentration of the alkyl halide only. Meanwhile, he discovered that primary and secondary alkyl halides, when reacting with nucleophiles, depend on both the concentration of the alkyl halide and the concentration of the nucleophile.
Starting around 1926, Ingold and Robert Robinson carried out a heated debate on the electronic theoretical approaches to organic reaction mechanisms. See, for example, the summary by Saltzman.
Ingold authored and co-authored 443 papers. Notable students include Peter de la Mare, Ronald Gillespie and Ronald Nyholm.