The company was established in London in 1883 as an agent for the American firm, Western Electric Company. The London operation sold US-designed telephones and exchanges to fledgling British telephone companies. A factory was established in North Woolwich to make lead-sheathed cables and manufacture equipment from components imported from the US. The company was closely involved in wireless broadcasting (radio). With its competitors it set up the BBC as well as producing wireless receivers. Valve technology was developed and commercially exploited.
In 1925 the company was acquired by International Telephone & Telegraph (ITT) who renamed the UK operation Standard Telephones & Cables. Within a few years, multi-channel transmission (1932), microwave transmission (1934), coaxial cabling (1936), the entire radio systems for the liners Queen Mary and Queen Elizabeth (1936-1939), the patenting of pulse code modulation (1938) all contributed to the hey-day of telephony's development.
Between 1939 and 1945 significant military work was undertaken with many developments particularly with regard to aerial warfare. In the 1950s the steady spread of TV transmission and availability in Britain very often used STC technology and equipment. STC became a major player in ship to ship and civil aviation communications, and the company opened a production unit in Southampton in 1956.
In the 1980s STC went into decline. An attempt to enter the mainframe computer market with the takeover of ICL led to financial strains. The company was eventually acquired by Northern Telecom (Nortel) in 1991.