Frank Williams had been running a Formula One operation since 1969, surviving on minimal funds through a succession of sponsor-labelled identities. After the Politoys-backed chassis era of 1972, both Motul and Politoys withdrew their support at the end of that season. Williams secured new backing from Marlboro and from Iso Autoveicoli, an Italian sports car company whose founder Renzo Rivolta saw value in the association with Formula One.
The existing Politoys FX3 chassis was reworked as the Iso-Marlboro FX3B, and a second car was built. Williams signed two new drivers for 1973: Howden Ganley from New Zealand and Nanni Galli from Italy.
The season opened in Argentina, where Galli qualified 16th and Ganley 19th and last on the grid. Galli's engine failed on the first lap while Ganley completed the race, though not classified due to finishing 17 laps adrift of the winner. Results improved somewhat in Brazil, with Ganley seventh and Galli ninth.
Galli was injured testing a sports car and missed several races. For the South African round his place was taken by local driver Jackie Pretorius, who retired with overheating. Ganley continued through the early season in the FX3B until new deformable structure regulations made the car obsolete. The reworked FX3B did appear in two non-championship events: Tony Trimmer took it to fourth place at the 1973 Race of Champions while Ganley retired.
A new car, the Iso-Marlboro IR, was introduced at the Spanish Grand Prix. The IR was driven by eight different drivers across the remainder of 1973. Ganley was the only regular, scoring a point at the Canadian Grand Prix. Of the other drivers who appeared — including Galli, Henri Pescarolo, Tom Belso, Graham McRae, Gijs van Lennep, Tim Schenken, and Jacky Ickx — only van Lennep added a point, at his home Dutch Grand Prix.
Both Iso Rivolta and Marlboro left before the 1974 season, ending the Iso-Marlboro name. Williams retained the two IR chassis, redesignating them as FW (standing for Frank Williams) to continue racing. The FW cars scored four points during 1974, including a fourth-place finish for Arturo Merzario in Italy, with Jacques Laffite joining Merzario as co-driver after three non-qualifications by the pay drivers initially engaged for the second seat.
The three Iso-Marlboro FW chassis used across 1974 were eventually renumbered as the Williams FW01, FW02, and FW03 for 1975, though they were essentially the same cars under different designations.
The Iso-Marlboro period represents the moment when Frank Williams' team first had enough resources to run two full-time cars consistently and develop a purpose-built chassis — the IR — rather than relying on an adapted customer design. The team remained well short of competitiveness but the structural experience gained during 1973 informed the years ahead. When Walter Wolf bought into the team before 1976, and when Williams subsequently departed to found Williams Grand Prix Engineering with Patrick Head in 1977, it was this lineage of incremental development and chassis construction that provided the foundation. The Iso-Marlboro name itself has no continuation beyond 1973, but it occupies a specific place in the origin story of one of the sport's great constructors.