The company was founded in 1859 when Alfred Charles Cossor began to manufacture scientific glassware in Clerkenwell, London. In 1875, Cossor's eldest son, also called Alfred Charles Cossor, joined the company and founded the electronics company. The electronic glassware such as cathode ray tubes and x-ray tubes, allowed the company to diversify into electronics which led to the production of a variety of items including valves, tubes, radio receivers, television receivers and radar equipment.

In the late 1950s, a reorganisation of the company formed a number of independent subsidiaries: Cossor Radio and Television Limited, Cossor Radar and Electronics Limited, Cossor Instruments Limited, and Cossor Communications Co Limited. In 1958, Cossor Radio and Television Limited was sold to Philips. Then, in 1961, Cossor was acquired by Raytheon.