Frank Williams had been running Formula One entries since 1969, starting with customer Brabham and March machinery. For 1973, after the withdrawal of Motul and Politoys, he negotiated a deal with Marlboro and with Iso Autoveicoli — the Italian manufacturer best known for its GT road cars including the Grifo — to provide financial backing and naming rights. The arrangement gave the team survival funding and a higher-profile identity without changing the technical direction: the cars continued to use Ford Cosworth DFV engines and Hewland gearboxes, the standard equipment shared by the majority of independent Formula One competitors.
The Iso–Marlboro campaign began with the reworked FX3B chassis, based on the Len Bailey-designed Politoys FX3 that had appeared in 1972. New drivers Howden Ganley of New Zealand and Italy's Nanni Galli were signed for the season. At the opening Argentine Grand Prix, Galli qualified 16th and Ganley 19th; Galli's engine failed on the first lap while Ganley finished but was not classified, being 17 laps down on the winner.
Results improved modestly in Brazil, with Ganley seventh and Galli ninth. Galli was then injured in a sports car testing accident and replaced by South African local Jackie Pretorius for the South African Grand Prix, where Pretorius retired with overheating while Ganley reached tenth, six laps adrift.
The FX3B was superseded mid-season by the new Iso–Marlboro IR, introduced at the Spanish Grand Prix. Eight different drivers raced the IR through the remainder of 1973. Ganley was the only consistent presence, scoring a point at the Canadian Grand Prix. Dutch driver Gijs van Lennep added another at his home race in the Netherlands. Of the other drivers — Nanni Galli, Henri Pescarolo, Tom Belse, Graham McRae, Tim Schenken, and Jacky Ickx — only van Lennep contributed to the points tally.
The FX3B also appeared in two non-championship races: at the Race of Champions, Tony Trimmer drove an FX3B to fourth place, while Ganley retired with handling problems. Ganley also retired at the BRDC International Trophy with low oil pressure.
Before the 1974 season, both Iso Rivolta and Marlboro withdrew their backing, leaving Williams without sponsors. The two IR chassis were retained and redesignated the FW — standing for Frank Williams — removing the Iso Marlboro branding and marking the formal end of the partnership. The cars raced in 1974 as the Williams FW, driven primarily by Arturo Merzario, with Laffite added as a second driver later in the year.
The Iso Marlboro team existed for only two seasons and scored a total of two championship points in its own name. Its significance lies less in results than in continuity: it kept Williams solvent and in the paddock during a difficult period, provided him with constructor status to retain for future seasons, and served as the chassis lineage from which the FW01, FW02, and FW03 designations evolved directly. The personnel and infrastructure developed under the Iso Marlboro banner fed into the team that, reborn as Williams Grand Prix Engineering in 1977, would become one of the most formidable constructors in Formula One history.