George Thomson was the son of J. J. Thomson, the discoverer of the electron. He was born in Cambridge and educated at the university there, where he taught (1914–22). He was then appointed to the chair of physics at Aberdeen University. Thomson moved to take the chair of physics at Imperial College, London, in 1930. He remained there until 1952 when he returned to Cambridge as master of Corpus Christi College, a position he held until his retirement in 1962.

His early work was in investigating isotopic composition by a mass spectrograph method. In 1927 he also performed a classic experiment in which he passed electrons through a thin gold foil onto a photographic plate behind the foil. The plate revealed a diffraction pattern, a series of concentric circles with alternate darker and lighter rings. The experiment provided crucial evidence of the wave–particle duality of the electron. Thomson shared the 1937 Nobel Prize for physics for this work with Clinton J. Davisson who had made a similar discovery independently in the same year.

During World War II Thomson was chairman of the ‘Maud committee’ to advise the British government on the atom bomb. (The name of this committee arose from a telegram message that Niels Bohr had managed to convey to England shortly after the German invasion of Denmark. To assure his friends of his well-being he instructed: “Please inform Cockroft and Maud Ray, Kent,” which was mistakenly interpreted as a secret message to ‘make uranium day and night’; Maud Ray was Bohr's former governess.) It was this committee that, in 1941, gave the crucial advice to Churchill that it was indeed possible to make an effective uranium bomb and elicited from him the minute: “Although personally I am quite content with existing explosives, I feel that we must not stand in the path of improvement.”