John Cockcroft was born at Todmorden [Lancashire] on 27 May 1897, the son of J. A. Cockcroft and A. M. Fielden. He was educated at Todmorden Secondary School, studying physics at the University of Manchester for a year before joining up as a signaller in the Royal Field Artillery in 1915, then being taken on as a college apprentice at Metropolitan-Vickers and sent back to Manchester University, where he took his B.Sc and M.Sc Tech. In 1921 Cockcroft moved on to St John’s College, Cambridge, and was a Fellow of St John’s College, Cambridge between 1928 and 1946. In 1925 he married E. Elizabeth Crabtree; they had one son and four daughters.

After graduating, Cockcroft worked as a research student at the Cavendish Laboratory in Cambridge, gaining his Ph.D in 1928. In 1932 he and E T S Walton succeeded in splitting atomic nuclei; Cockcroft was also made Jacksonian Professor of Natural Philosophy at Cambridge, (1939-1946). During the war, Cockcroft was Chief Superintendent at the Air Defence, Research and Development Establishment, Ministry of Supply, (1941-1944), then Director of the Atomic Energy Division, National Research Council of Canada, (1944-1946). Returning to Britain, he then took up the post of Director of the Atomic Energy Research Establishment, Ministry of Supply, at Harwell, (1946-1958).

Cockcroft was a member of many bodies, including: Chairman of the Defence Research Policy Committee and Scientific Adviser to the Ministry of Defence, (1952-1954); Member, Advisory Council on Scientific Policy until 1963; Member for Scientific Research, United Kingdom Atomic Energy Authority, (1954-1959) (Part-time member, 1959). He was Master of Churchill College, Cambridge, from 1959 until his death, and among his many honours, was awarded the Nobel prize for physics (with E. T. S. Walton) in 1951.

Cockcroft's publications include: various papers on nuclear physics in Proceedings of the Royal Society; also on technical subjects, Journal of the Institute of Electrical Engineers.

He died on 18 September 1967.