The C9's chassis retained much of its predecessor's aluminium monocoque structure but was considerably stiffer and incorporated numerous detail improvements. Rear suspension was revised from vertically positioned spring-and-damper units over the top of the gearbox to a horizontal layout aligned with the car's longitudinal axis. Aerodynamically, the oil and water radiators were repositioned to the nose, which allowed a modified splitter plate and the removal of large NACA ducts from the door sills. The rear deck was re-profiled and the rear wing mounted on a single central support.
Two aerodynamic configurations were used: a high-downforce sprint setup generating 2,222 kg of downforce at 320 km/h, and a low-drag version for the Mulsanne Straight at Le Mans. Early engines were prepared by Swiss specialist Heini Mader, though this was later understood to mask Mercedes-Benz's back-door involvement. The engine was progressively developed, with new crankshafts, higher-efficiency KKK turbochargers, and a liner-less block. On 2.2 bar of boost the unit was said to produce close to 800 hp. Maximum race boost was 1.9 bar at a general race ceiling of 6,500 rpm. For 1989, a switch to the M119 engine with 16-valve aluminium heads raised output by around 20 hp to approximately 720 hp at 1.6 bar, while also improving fuel efficiency enough to allow the boost to be taken to around 820 hp.
For its debut season the C9 was run by Kouros Racing, named after the fragrance brand of parent company Yves Saint Laurent, with semi-official Mercedes backing. The arrangement covered five races. Results were modest — points scored in only one round, a twelfth in the teams' standings — though the car's potential was evident. Jean-Louis Schlesser won the non-championship Nurburgring Supercup, the team's sole victory of the year.
For 1988, the Kouros sponsorship ended and the team was renamed Sauber Mercedes. A change of senior management at Mercedes, led by new deputy chairman Professor Werner Niefer, brought full factory support. AEG-Olympia took over as title sponsor, AEG being a Daimler-Benz subsidiary. Former BMW M team manager Jochen Neerpasch and Swiss former driver Max Welti joined the management team. The C9 won five races and finished second in the championship behind the Jaguar XJR-9, though the season included a significant setback at Le Mans when the team withdrew after Klaus Niedzwiedzi suffered a tyre blow-out at high speed and Michelin could not guarantee the remainder of the race.
The 1989 season brought a change to Mercedes' traditional silver livery and an upgrade to the M119 engine. The C9 won all but one race of the season — the only defeat came at Dijon, where the Joest Porsche 962 of Bob Wollek and Frank Jelinski prevailed. At Le Mans, the Baldi/Acheson/Brancatelli car recorded 400 km/h on the Mulsanne Straight during qualifying, one of the highest speeds in the race's history to that point, exceeded only by the purpose-built WM Peugeot P88. The three C9s finished first, second, and fifth in the race. Jean-Louis Schlesser won the drivers' championship. The C9's combination of outright pace and remarkable reliability — it failed to finish only twice all season, and on both occasions the race was won by the sister car — set it apart from its rivals.
The C9 was replaced by the Mercedes-Benz C11 from the second race of the 1990 season, though it took one final victory in the opening round. A total of six chassis were built.
The Sauber C9 was awarded the Autosport Awards Racing Car of the Year for 1989. Its 400 km/h qualifying runs at Le Mans, combined with similar speeds from the WM Peugeot P88, directly prompted the ACO to introduce two chicanes on the Mulsanne Straight from 1990 onwards, ending the era of unlimited top speeds on that famous stretch of road. The car later appeared in video games including Gran Turismo and Forza Motorsport, maintaining its profile as one of the definitive Group C machines.