Before finishing his doctorate, he developed and published methods to detect antibodies with Arthur Mourant and Robert Russell Race in 1945.

[5] Coombs became a professor and researcher at the Department of Pathology of University of Cambridge, becoming a Fellow of Corpus Christi College, and a founder of its Division of Immunology.

[6] In November 1956, Coombs founded the British Society for Immunology alongside John H. Humphrey, Bob White, and Avrion Mitchison.

[5] The Coombs test, which he developed and published together with Arthur Mourant and Robert Russell Race in 1945, has formed the base of a large number of laboratory investigations in the fields of hematology and immunology.

Wells he put forward an explanation of sudden infant death syndrome (SIDS) as an anaphylactic reaction to dairy proteins.