Forti co-founded Forti Corse in the late 1970s alongside businessman Paolo Guerci, establishing the team in Alessandria in northern Italy. The operation initially competed in Italian and European Formula Ford and Formula Three, where it quickly became a regular contender. Forti's eye for driver talent and organisational capability helped nurture several drivers who went on to Formula One careers, including Franco Forini, Enrico Bertaggia, Emanuele Naspetti, and Gianni Morbidelli — each of whom won Italian Formula Three titles with the team.
From 1987, Forti guided his team into International Formula 3000. The debut season was unspectacular, with Nicola Larini and Nicola Tesini driving a Dallara chassis in an unfamiliar category, but the organisation steadily improved. The team's first Formula 3000 victory came in 1990 with Morbidelli behind the wheel. Over the following years Forti Corse accumulated nine victories in the championship, establishing itself as one of the most experienced and capable squads in the category. By 1994, Forti had decided that season would be the last in Formula 3000, as plans for an F1 entry were taking shape.
Forti had been studying the possibility of entering Formula One since 1991, mindful of teams like Coloni and Onyx that had made the step prematurely and failed. He pursued financial backing as the primary prerequisite for a sustainable campaign. A deal with wealthy Brazilian driver Pedro Diniz, engineered through Italian-Brazilian businessman Carlo Gancia who replaced co-founder Guerci as a team stakeholder, provided the platform. The Diniz family's retail connections secured sponsorship from major Brazilian and multinational brands, giving the team a claimed first-year budget of around $17 million and a planned three-year commitment.
Forti's F1 car, the FG01, debuted in 1995 and was widely criticised as overweight and uncompetitive. Forti managed the team through a season spent firmly at the back of the grid, but achieved a measure of development progress and a stable finishing record. When Diniz left for Ligier ahead of 1996 and took the bulk of the team's sponsorship with him, the project was placed under severe financial strain. Forti pressed on, introducing the improved FG03 chassis mid-season, but debts to engine supplier Cosworth proved terminal.
In an effort to save the team, Forti agreed to sell a 51 per cent stake to an entity called Shannon Racing, a Milanese financial group with Irish registration. He subsequently alleged that Shannon had failed to pay within the agreed six-day deadline and contested their ownership claim through the Italian courts. The legal dispute ran alongside the team's collapse mid-season: both cars sat unassembled at the German Grand Prix, and Forti did not return to the championship thereafter. Shannon eventually won the court case in September 1996, but by that point the team had ceased to operate entirely.
Following the collapse of his Formula One team, Forti remained connected to motor racing at a lower level. In 2003 he was employed by a Euro Formula 3000 team, his last known involvement in the sport. Guido Forti died on 11 January 2013 in Alessandria, aged 72.