BA Oxford 1936, BSc 1937, BM BCh 1939, MA 1940, DM 1946; MD Cambridge 1946.
Mills was born in Birmingham on 28 June 1914, the son of George Percival Mills, a consultant surgeon. He gained his medical education at Oxford and Birmingham. Mills was lecturer at New College Oxford and at Jesus College Cambridge before being appointed lecturer in physiology at the University of Manchester. He was promoted to senior lecturer in 1955, reader in 1959 and in 1965 he became Brackenbury Professor of Physiology. Mills was internationally renowned for his research into human circadian rhythms. He studied the effects of this 'internal clock' on performance, and built an isolation unit at Risley, near Warrington. Mills was a member of MMS, the Physiological Society and the Renal Association. He was a fellow of the Linnean Society and was a keen botanist and mountaineer. He died in a mountaineering accident on 3 December 1977, just months before he had planned to retire.