The first XJ-S appeared in 1975 as a 1976 model. Power came from the Jaguar V-12 petrol engine with a choice of a manual or automatic transmission, but the manual was soon dropped. V-12 automobiles were unusual at the time, with notable others coming from Italian luxury sports car makers Lamborghini and Ferrari. The specifications of the XJ-S compared well with both Italian cars; it was able to accelerate to 60mph (97km/h) in 8.9 seconds and reach 142mph (229km/h). The first series of XJ-S cars had a Borg-Warner Model 12 transmission with a cast iron case and a bolt-on bell-housing. In 1979 GM Turbo-Hydromatic 400 transmissions were fitted. The TH400 transmission was an all aluminium alloy case with an integrated non-detachable bell-housing.
Jaguar's timing was not good; the car was launched in the wake of a fuel crisis, and the market for a 5.3-litre V12 grand tourer was very small. The styling was also the subject of criticism, including the "flying buttresses" behind the windows.
Jaguar did seize promotional opportunities with the television series The New Avengers and Return of the Saint. The New Avengers featured Mike Gambit (Gareth Hunt) who drove an XJ-S. Return of the Saint saw Simon Templar (played by Ian Ogilvy) driving an early XJ-S with the number plate "ST 1". Miniature versions were made by Corgi and proved popular. A decade and a half before, Jaguar had turned down the producers of the earlier Saint series when approached about the E-type; the producers had instead used a Volvo P1800.
Responding to criticisms that the XJ-S was not a worthy E-type successor, Pininfarina revealed a sporty show car in 1978 based on XJ-S mechanicals and called Jaguar XJSpider. The car never went into production.
From July 1981, XJ-S received the new High-Efficiency engine for much better economy; as a by-product, power was increased to 220kW (295hp) or 196kW (263hp) in North America. At the same time, the XJ-S received changes to its exterior and interior (new five-spoke alloy wheels, chrome inserts on the upper part of the bumpers, wood inserts on dashboard and door cappings). In 1982, the new V12 XJ-S won first and second at the RAC Tourist Trophy race at Silverstone.