He spent much of his career at Brunner Mond and its successor Imperial Chemical Industries, as chief chemist, research manager and in a recruiting capacity, with particular knowledge of phase rule chemistry, and developed many processes related to the manufacture of explosives.
His father was a master mariner and was an officer in the Royal Naval Reserve; his great-grandfather, James Freeth, was Quartermaster General between 1851 and 1854, and his grandfather was a major-general as well.
[3][6][8] At the outbreak of World War I, Freeth was in the Territorial Army, having joined in 1912, and spent six weeks in the trenches in France with the Cheshire Regiment as a major[9] in early 1915, but was then sent back to Britain to continue his armaments research at Brunner Mond at the direction of Lord Moulton.
Freeth built upon his pre-war work and implemented two processes he had devised in 1909 at an industrial scale in plants at Lostock Gralam, Sandbach and a specialised factory in Swindon.
A number of Brunner Mond (and Imperial Chemical Industries) recruits went the other way, to the Netherlands to work with Onnes and increase the fruitful cross-pollination.
[3][20][21] Freeth was awarded a doctorate of the University of Leiden in 1924—only possible thanks to a special decree of the Dutch Parliament—and joined the Royal Society in 1926 on the recommendation of Donnan and Lord Moulton.
[23] During World War II, Freeth undertook secret research for the Special Operations Executive, including developing materials for field use or for sabotage by commandos or resistance groups.
[24] During this period of activity, he re-connected with friends within ICI and returned to the company as a University Liaison Officer on 1 February 1944, recruiting fresh talent for industrial chemical research.