Imperial Chemical Industries plc came into existence in 1926, following the merger of Nobel Industries Ltd, Brunner, Mond and Company Ltd, the United Alkali Company, and the British Dyestuffs Corporation. The new company was called Imperial Chemical Industries Ltd. Its operations began in 1927, with 33,000 people employed in five main product areas: alkali products, explosives, metals, general chemicals, and dyestuffs. In 1928, its head office opened in Millbank, London. The former British Dyestuffs Corporation works at Blackley, Manchester became the home of ICI's Dyestuffs Division. The main factory for the General Chemicals Division was at Billingham, County Durham.

ICI's Research and Development Department developed a number of significant products in the early 20th century, including the acrylic plastic Perspex in 1932, Dulux paint (in partnership with DuPont) in 1932, polyethylene in 1937 and polyethylene terephthalate fibre (known as Terylene and PET) in 1941.

The work on polyethylene was led by the Dyestuffs Division at Blackley until a new Plastics Division was established at Welwyn Garden City in 1937. In 1971, the Dyestuffs Division merged with parts of the Nobel Division to become known as the Organics Division. Later mergers with other specialty chemical producers created ICI Colours and Fine Chemicals, which then became ICI Specialties.

From 1940, ICI Dyestuffs was involved in the manufacture of Nylon fabrics at its Huddersfield plant, and in 1964 the company established ICI Fibres to manage its successful textile, fibres and Nylon production. The Nylon part of the business was sold to DuPont in 1992.

In 1944, as Imperial Chemical (Pharmaceuticals) Ltd, the company was involved in the development of penicillin at its Trafford Park works. Because of its success with pharmaceuticals, the company established ICI Pharmaceuticals in 1957. In 1993, ICI Pharmaceuticals and other bioscience divisions became Zeneca, along with ICI Specialties. Zeneca merged with Astra AB in 1994 to form Astra Zeneca Plc.

General Chemical production continued until the acquisition of ICI by Akzo Nobel in 2007.