Cronin graduated in 1951 his studies at Southern Methodist University and went for further training at the University of Chicago, where he received his doctorate in 1955. He then worked at Brookhaven National Laboratory. 1958 to 1971 he was at Princeton University and then became a professor at the University of Chicago.
Cronin worked for decay of hyperons and for the production of muons. He determined the total cross section of the pion -proton scattering and perfected the spark chamber, which he used as the first physicist to detect particles by photographing the radio tracks.
Subject of current research in particle physics is the Cronin effect. He describes the modification of hadron scattering on nuclei compared to what one would expect when considering the core as a set of independent nucleons.
Cronin received in 1980 along with Val Fitch the Nobel Prize in Physics "for the discovery of violations of fundamental symmetry principles in the decay of neutral K- mesons ". The experiment was established in 1964 to run at Brookhaven National laboratory.
Later he worked on the study of cosmic rays at the Pierre Auger Observatory.