Thomson was born in Cambridge in 1892, into a family of scientific distinction on both sides. His father, Sir Joseph Thomson (always known as `J.J.'), was one of the foremost physicists of the day, Director of the Cavendish Laboratory, Cambridge, and in 1906 awarded the Nobel Prize for Physics for his discovery of the electron. His son George was much guided and influenced by his father, conducting early collaborative research with him and having access through him to current work on the frontiers of knowledge, as his later historical writings frequently testify. Thomson's collaboration with his father continued for many years and included joint work on the Third (1928) Edition of Conduction of Electricity through Gases.
After education at the Perse School and Trinity College, Cambridge, Thomson began research in 1913 at the Cavendish Laboratory under his father's supervision, and was elected a Fellow of Corpus Christi College in 1914. During the First World War he was attached to the Royal Flying Corps at the Royal Aircraft Factory (later Establishment) at Farnborough, where he was a member of the famous `Chudleigh Mess' and formed lasting friendships with F.W. Aston, W.S. Farren, B.M. Jones, F.A. Lindemann (later Lord Cherwell), G.I. Taylor and others.
At the end of the War he returned to Cambridge, and in 1922 was appointed Professor of Natural Philosophy at the University of Aberdeen. Here his most famous work was done, on electron diffraction by thin films (1926-28), for which he shared with C.J. Davisson the Nobel Prize for Physics in 1937.
In 1930, after a visit to America lecturing and working at Cornell, Thomson, now a Fellow of the Royal Society, moved to London as Professor of Physics at Imperial College. He continued work on electron diffraction and tried to develop it as a research tool for the study of surfaces, and also encouraged electron microscopy. A protracted illness which declared itself early in 1936 seriously interrupted his experimental work and marked the effective end of his work on electrons. Instead, he pursued the interest in nuclear physics begun a few years earlier, and in 1939 was quick to see the possible military implications of current work in nuclear fission. His professional knowledge, and his personal acquaintance with leading scientists and government advisers enabled him to initiate investigations, especially as (from April 1940) Chairman of the MAUD Committee which reported on the feasibility of an atomic weapon.
During the Second World War, subsequent to his work on the MAUD Committee, and after two years at the Royal Aircraft Establishment, Farnborough, Thomson was sent as Scientific Liaison Officer to Canada. At this time, his wife Kathleen was seriously ill in America; her death at the end of 1941 was a great blow to him. He remained in Canada until summer 1942 after which he returned to Britain to become Deputy Chairman of the Radio Board (1942-43) and Scientific Adviser to the Air Ministry (1943-44). He resigned this post in December 1944 to resume work at Imperial College. He was knighted in 1943.
His scientific interests now centred on the study of cosmic rays and mesons, and on nuclear fusion - itself a development of a theory of an electrodeless discharge put forward by `J.J.'. Under Thomson's guidance, work on an electrodeless torus proceeded at Imperial College and was provisionally patented in 1946; the team subsequently transferred to the A.E.I. laboratories at Aldermaston, while similar work was also in progress at Harwell. Both groups produced an apparatus - SCEPTRE at A.E.I., ZETA at Harwell - which attracted much attention when they were brought to the notice of the general public in 1958.
In 1952 Thomson returned to Corpus Christi College, Cambridge, as Master; he remained there until 1962 and spent his retirement in Cambridge, where he died in 1975.