Mercedes-Benz unveiled the W140 S-Class at Geneva International Motor Show in March 1991, with the sales starting in April 1991 and North American launch was on 6 August 1991.

Several engineering prototypes were evaluated from early 1987, with the final exterior design locked in September 1987.

Innovative metal-forming technology allowed the extension of the engine hood/bonnet to the front bumper, with the grille placed inside the extruded metal.

The project's cost overruns and eighteen-month delay resulted in the departure of Wolfgang Peter, the chief engineer of Mercedes-Benz.

[7] The price of a W140 was considerably higher than its predecessor, the W126 (up to 25 per cent), leading to slow sales during the recession of 1990-1994.

The slow sales of the W140 can also be attributed to a wave of Japanese luxury cars that were introduced before the W140 was launched.

Many enthusiasts argue that the W140 was the "last true S-Class," as its successor, the W220, was criticized for having inferior engineering, and in the case of early models, poor reliability.

Due to the increasing concern for climate protection and fear of sending a wrong message to the public in the early 1990s, the V16 engine was quietly cancelled.

In 1995, the two tone exterior appearance was made to be monotone, low-beam xenon headlamps were added and the rear indicator lenses became clear.

The W140 received notoriety in 1997 when Diana, Princess of Wales died in a car crash, involving an S 280 model, in a Paris tunnel.

The Sultan of Brunei ordered eighteen S 73 T station wagons/estates with AMG-prepared M120 7.3-litre V12 engines producing 391 kW (532 PS; 524 hp) and 750 N⋅m (550 lb⋅ft) to be built, with ten units delivered.

[12] A one-off custom-built S 500 lang Landaulet Popemobile was built for Pope John Paul II in 1997.

In 1994, AMG developed a 6.0-litre version (M 119 E 60) with 279 kW (379 PS; 374 bhp) and 580 N⋅m (428 lb⋅ft) in a very limited production for Japanese market.

An AMG-prepared 6.0-litre M 120 V12 with higher performance rating, 327 kW (445 PS; 439 hp) and 623 N⋅m (460 lb⋅ft), was only available for S- or CL-Class (C140) coupes and not S-Class sedans/saloons.

In September 1995, the 5G-Tronic was updated with electronic control for more optimal shifting points based on the sensor readings and became the sole automatic transmission option for the entire model range from 1996 to 1998.