Thomson was born in Cambridge, England, the son of Physicist and Nobel laureate J. J. Thomson and Rose Elisabeth Paget, daughter of George Edward Paget. Thomson went to The Perse School, Cambridge before going on to read mathematics and physics at Trinity College, Cambridge, until the outbreak of World War I in 1914, when he was commissioned into the Queen's Royal West Surrey Regiment. After brief Service in France, he worked on aerodynamics at Farnborough and elsewhere. He resigned his commission as a Captain in 1920.