In 1961, Citroën began work on 'Project S' – a sports variant of the Citroën DS. As was customary for the firm, many running concept vehicles were developed, increasingly complex and upmarket from the DS.[2] At some stage in the 9-year project, it evolved from developing a faster variant of the 1955 DS to developing an entirely new, thoroughly engineered car – in terms of engineering effort, a replacement for the high volume DS model. Citroën purchased Maserati in 1968 with the intention of harnessing Maserati's high-performance engine technology to produce a true Gran Turismo car, combining the sophisticated Citroën suspension with a Maserati V6.[3]

The result was the Citroën SM, first shown at the Geneva Motor Show in March 1970. It went on sale in France in September of that year. Factory produced cars were all left-hand-drive, although RHD conversions were done in the UK and Australia.

This car was unusual for France – production of luxury cars was heavily restricted in the country by post-World War II puissance fiscale horsepower tax, so France had not had a production vehicle in this market sector since before World War II.[4] The SM had an engine of only 2.7 liters owing to these regulations; it was the first response to the luxury/performance sector since the export oriented Chrysler V8 engine Facel Vega in the late 1950s.[5] Citroën's flagship vehicle competed with high-performance GTs of the time from other nations and manufacturers, such as Jaguar, Lotus, Ferrari, Aston Martin, Alfa Romeo, Mercedes-Benz, and Porsche.

The origin of the model name 'SM' is not completely clear. The 'S' may derive from the Project 'S' designation, the aim of which was to produce what is essentially a sports variant of the Citroën DS, and the 'M' perhaps refers to Maserati, hence SM is often assumed to stand for "Systeme Maserati" or "Sports Maserati". Another common alternative is Série Maserati,[6][7] but others have suggested it is short for 'Sa Majesté' (Her Majesty in French), which aligns with the common DS model's nickname 'La déesse' (The Goddess).

The SM did not find a sufficient customer base in the small European GT market, but much of the SM's technology was carried forward to the successful Citroën CX, launched in 1974 the DIRAVI steering being the most obvious example. The same basic engine in enlarged 3.0 L form (some in Italy had 2.0 L) was used in Maserati's own Merak (1,800 units) and later with some modification in the Biturbo (40,000 units).[8] The Merak, Khamsin, and Bora, used Citroën's high-pressure hydraulics for some functions, and the Citroën gearbox in the Merak, during the Citroën-Maserati alliance