Siddeley Autocars, of Coventry, was founded by John Davenport Siddeley in 1902. Its products were heavily based on Peugeots, using many of their parts but fitted with English-built bodies. This company merged with Wolseley in 1905 and made stately Wolseley-Siddeley motorcars. They were used by Queen Alexandra and the Duke of York later King George V.
In 1909 J. D. Siddeley resigned from Wolseley and took over the Deasy Motor Company, and the company became known as Siddeley-Deasy. In 1912, the cars used the slogan "As silent as the Sphinx" and started to sport a Sphinx as a bonnet ornament, a symbol that became synonymous with descendent companies.
In April 1919 Siddeley-Deasy was bought out by Armstrong Whitworth Development Company of Newcastle upon Tyne and in May 1919 became Armstrong Siddeley Motors Ltd, a subsidiary with J. D. Siddeley as managing director. In 1927, Armstrong Whitworth merged its heavy engineering interests with Vickers to form Vickers-Armstrongs. At this point, J. D. Siddeley bought Armstrong Siddeley and Armstrong Whitworth Aircraft into his control. In 1928, Armstrong Siddeley Holdings bought Avro from Crossley Motors. Also that year Siddeley partnered with Walter Gordon Wilson, inventor of the pre-selector gearbox, to create Improved Gears Ltd, which later became Self-Changing Gears – the gearbox that should be credited with enabling the marketing tagline "Cars for the daughters of gentlemen".
The first car produced from the union was a fairly massive machine, a 5-litre 30 hp. A smaller 18 hp appeared in 1922 and a 2-litre 14 hp was introduced in 1923. 1928 saw the company's first 15 hp six; 1929 saw the introduction of a 12 hp vehicle. This was a pioneering year for the marque, during which it first offered the Wilson preselector gearbox as an optional extra; it became standard issue on all cars from 1933. In 1930 the company marketed four models, of 12, 15, 20, and 30 hp, the last costing £1450.
The company's rather staid image was endorsed during the 1930s by the introduction of a range of six-cylinder cars with ohv engines, though a four-cylinder 12 hp was kept in production until 1936. In 1933, the 5-litre six-cylinder Siddeley Special was announced, featuring a Hiduminium aluminium alloy engine; this model cost £950. Car production continued at a reduced rate throughout 1940, and a few were assembled in 1941.
The week that World War II ended in Europe, Armstrong Siddeley introduced its first post-war models; these were the Lancaster four-door saloon and the Hurricane drophead coupe. The names of these models echoed the names of aircraft produced by the Hawker Siddeley Group (the name adopted by the company in 1935) during the war. These cars all used a 2-litre six-cylinder engines, increased to 2.3-litre engines in 1949. From 1953 the company produced the Sapphire, with a 3.4-litre six-cylinder engine.
The last model produced by Armstrong Siddeley was 1958's Star Sapphire, with a 4-litre engine, and automatic transmission. The Armstrong Siddeley was a casualty of the 1960 merger with Bristol; the last car left the Coventry factory in 1960.