The IR was created to replace the existing Iso-Marlboro FX3B, which failed to comply with the deformable structure regulations introduced for the 1973 season. John Clarke, a former March engineer, designed the new car along conventional lines — wedge-shaped and low-slung, following the influential thinking of the Lotus 72 and McLaren M23. It featured double wishbone front suspension, upper and lower links at the rear, and outboard springs throughout. Fuel tanks were positioned on either side of the cockpit. The initials "IR" stood for Iso Rivolta, acknowledging the Italian car manufacturer whose name appeared on the car, though Iso played no role in the car's actual development. During the 1973 season, Italian engineer Giampaolo Dallara was brought in to revise the rear suspension, and Ron Tauranac also contributed development work.
The IR debuted at the Spanish Grand Prix, the fourth round of 1973, with Howden Ganley and Nanni Galli as drivers. The team operated on limited resources, cycling through a series of pay drivers for the second seat after Galli retired from racing. A rotating cast of drivers including Henri Pescarolo, Graham McRae, Gijs van Lennep, Tim Schenken, and Jackie Ickx took turns alongside Ganley throughout the year.
The car's most memorable moment came at the Canadian Grand Prix, held in wet conditions that triggered the first safety car deployment in Formula One history — a Porsche 914 driven by Eppie Wietzes. After race order chaos, Ganley found himself leading for eight laps. He was eventually passed by Emerson Fittipaldi and Jackie Stewart but finished sixth, sparking debate about the true race classification. Van Lennep's sixth at the Dutch Grand Prix had earlier earned the team's first World Championship point. The IR closed the season having scored two championship points and placed Williams tenth in the Constructors' standings.
When both Marlboro and Iso withdrew their backing before the 1974 season, the revised car was renamed the Iso-Marlboro FW. Frank Williams ran a reduced operation, initially fielding a single car for Arturo Merzario, who had replaced Ganley. A third chassis was completed during the season to allow a spare. Jacques Laffite joined as second driver from the German Grand Prix onwards.
Merzario delivered the season's standout result at the Italian Grand Prix, finishing fourth to score three points, the car's best result under any of its three designations. The team accumulated four championship points across the campaign, again taking tenth in the Constructors' Championship.
The three surviving FW chassis were renamed Williams FW01, FW02, and FW03 for 1975, though all were mechanically the same car updated by Ray Stokoe. Both Merzario and Laffite remained with the team. The design was by now becoming dated, and a replacement — the Williams FW04 — was introduced from the Spanish Grand Prix. The FW03 continued to circulate in the hands of a string of one-race drivers including Tony Brise, Ian Ashley, Jo Vonlanthen, and Renzo Zorzi, but scored no points. All of Williams's six championship points in 1975 were scored by the new FW04. The FW03 was retired before the United States Grand Prix.
Frank Williams sold the FW03 to Swiss entrant Loris Kessel in 1976, who extensively modified the car and renamed it the Apollon. Kessel attempted to enter the car at the 1976 and 1977 Italian Grands Prix but did not race on either occasion, failing to qualify in 1977 by over six seconds before crashing in the final qualifying session.
The Iso-Marlboro IR and its successors chart the survival-era origins of Frank Williams's eventual championship-winning team. Williams operated under perpetual financial pressure, relying on pay drivers and second-hand tyres, yet still managed to score championship points across three seasons with essentially the same basic chassis. The car's competitive highlight — Ganley's near-win in Canada — remains a curiosity in Formula One's historical footnotes, and Merzario's fourth at Monza in 1974 proved that the design had genuine pace when conditions aligned.