It was the first Jaguar XJ produced entirely under Ford Motor Company ownership, and can be considered an evolution of the outgoing XJ40 generation.

[2][3] At the car's launch in October 1994 at the Paris Motor Show, Jaguar marketing material made use of the phrase "New Series XJ" to describe the X300 models.

[4] The program introduced state-of-the-art automated body welding robots manufactured by Nissan, and was intended to show the future direction of the British auto industry.

Early X300 cars were built without a front passenger glove-box, due to space constraints caused by the introduction of a front-passenger airbag.

Ford halted development of the saloon, termed XJ90, and proposed to install its new engine and front and rear ends onto the centre section of the XJ40 model; however, the V8 was not ready, and would not be so until after the X300's successor, the XJ X308.

A visibly significant chromed pipe connecting the left and the right banks of the V12 in the XJ40 platform (intended to vent and route the crankcase blow-by gas to the intake plenum) was changed with the introduction of the X300 to an almost invisible design at the top center of the engine underneath a plastic cover that also hides fuel rails and coilpacks.

The normally aspirated six-cylinder X300 cars used either a ZF four-speed automatic gearbox (4HP-22 on the 3.2 L and 4HP-24 on the 4.0 L),[6] or a Getrag 290 five-speed manual.

This switch is replaced with a blanking plate on the 3.2 L. The supercharged six-cylinder engine in the XJR was normally built with the optional GM 4L80-E four-speed automatic and very few XJRs were ordered with the standard specification Getrag 290.

According to David Versical of Automotive News, Ford's influence was evident more in terms of "product development processes than its parts bin".

For example, the North American XJ6 was only available with the 4.0 L engine, and all cars sold there were equipped with alloy wheels, a leather interior, and air conditioning.

On these base cars, aluminium alloy wheels, leather upholstery, and air conditioning were all extra-cost options.

To attract younger buyers, Jaguar offered a Sport model with wider 18-inch wheels, revised seats, and stiffer suspension.

Rain gutters and window surrounds were matte black, except on North American models where they were polished stainless steel.

The XJ12 model, which carries the code name X305 along with the short wheel base Daimler Double Six, featured the same trim level of the Sovereign but was powered by the 6.0 L version of the Jaguar V12 engine.

The X305 was equipped with an On-Board Diagnostics System; however, it failed to fully meet the OBD-II specifications, which became mandatory for the 1996 model year in the United States.

In 2001, the United States EPA and Jaguar Cars entered into a settlement that extended the emissions warranty on 1995 and 1996 model year XJ12 saloon cars to 14 years or 150,000 miles due to their non-compliant NipponDenso Engine Management System, which was unable to provide continuous misfire monitoring, a requirement for OBDII compliance.

Vanden Plas X300 cars in the United States after MY 1995 are all built on the long-wheelbase body shell, although they were only available with the six-cylinder engine, leaving the V12 available solely in the XJ12 model for that market.

When the dealership refused to honor the advertised price, and later sold the car to someone else for US$38,399, the ensuing lawsuit went up on appeal to the Supreme Court of California.

The Century was equipped with all features and upgrades available on the X300 cars, plus chromed wheels, special exterior paint, and electrically adjustable rear seats.

Successive versions of the XJ were used as the prime ministerial car by Gordon Brown, David Cameron, Theresa May, and Boris Johnson.