Williams entered 1988 without the Honda turbo engines that had powered their 1986 and 1987 Constructors' Championship-winning cars, a partnership that had soured partly due to disputes over driver contracts and internal politics. Switching to the naturally aspirated Judd CV V8 for the FW12, the team found the car sluggish in a straight line, its reactive suspension system adding weight and sapping power from the modest Judd unit. Early in the season, drivers Nigel Mansell and Riccardo Patrese described the car as "pathetically slow in a straight line," a description borne out by speed trap figures showing the FW12 peaking around 265 km/h against the over 290 km/h of the Honda-powered rivals.
The reactive suspension, which had debuted on the FW11 at the 1987 Italian Grand Prix, caused unpredictable handling throughout 1988 as air entered the hydraulics and altered computerised settings mid-lap. At the British Grand Prix at Silverstone, Williams technical director Patrick Head made the decision to replace the system with conventional steel springs and dampers overnight before the race. Both Mansell and Patrese immediately improved their times dramatically, and Mansell drove to second place in the wet race.
Mansell missed the Belgian and Italian races through chickenpox, with Martin Brundle and Jean-Louis Schlesser substituting. Schlesser's sole F1 World Championship start ended in infamy when he collided with race leader Ayrton Senna at Monza on lap 49, handing Ferrari an emotional 1-2 result just a month after the death of Enzo Ferrari. Williams dropped to seventh in the Constructors' standings for 1988 with just 20 points.
During 1988, Williams negotiated an engine supply arrangement with Renault, who were returning to Formula One after withdrawing as a turbo engine supplier following 1986. Williams built a test mule, the FW12B, to accommodate the longer Renault V10, and the race-specification FW12C was prepared for 1989 — marking the first Renault-powered Williams Formula One car.
With Mansell departing for Ferrari, Thierry Boutsen joined Patrese for 1989. The FW12C showed genuine promise from the opening round in Brazil, where Patrese qualified second and led from the start, setting the fastest lap before retiring with a broken harmonic balancer. Patrese's Brazil drive equalled the then-record for Grand Prix starts, jointly held by Graham Hill and Jacques Laffite, at his 176th start.
The FW12C scored its sole victory at the 1989 Canadian Grand Prix, a rain-affected race in which Boutsen took his first Formula One win with Patrese second — Williams's first 1-2 result since the 1987 Mexican Grand Prix. Patrese had his strongest season to date, recording consecutive second-place finishes in Mexico, Phoenix, and Canada, along with a third in France. He also claimed the FW12C's only pole position at the Hungarian Grand Prix, leading comfortably until a radiator failure on lap 51 dropped him out of the points.
By the Italian Grand Prix at Monza, the Renault V10 engine was improving but the FW12C airframe had reached its development ceiling. McLaren with their Honda V10, Ferrari with their V12, and increasingly Benetton with the exclusive Ford V8 had moved ahead. Williams had already been developing the successor FW13, originally designed around the reactive suspension system and subsequently redesigned for passive suspension. After Boutsen finished third and Patrese fourth at Monza, the team introduced the FW13 for Portugal.
Patrese briefly returned to the FW12C for the Spanish Grand Prix, qualifying sixth and finishing fifth, making that the car's final Formula One race appearance. From Japan onward, Williams raced exclusively with the FW13.
A notable postscript to the FW12C's story came in December 1989, when 1976 World Champion James Hunt conducted a secret test of the car at the Paul Ricard Circuit, setting competitive times as a prelude to a potential comeback. He ultimately decided against returning to racing and remained with BBC Television.
Overall, across the Judd-powered FW12 and Renault-powered FW12C, the cars scored one win, one pole position, two fastest laps, and nine podium finishes across 29 races. The programme laid the groundwork for the Williams-Renault partnership that would dominate the early 1990s.