H W Sullivan Limited was established in 1897 by Herbert Watson Sullivan. The company initially produced telegraph signalling equipment such as Wheatstone bridges and Kelvin bridges before focusing on precision electrical equipment. Before establishing the company, Sullivan worked for a number of electrical companies including spending 20 years as electrician-in-chief and consulting engineer in the undersea cable lying industry.

In 1922, the company was incorporated as a limited company, trading as H W Sullivan Ltd. based at 19 Great Winchester St., London E.C., Liverpool House, Middlesex Street, London E1 and Leo Street, London E15. In 1967, the company was taken over by Cambridge Instrument Company, keeping their original name. The company was taken over again in 1971 by Thorn but kept its brand until 1987.