Rumi's family had deep roots in metalworking. His grandfather, also named Gabriele Rumi, founded an iron foundry in Brescia. Gabriele Rumi the younger took over the running of the business in 1961 and began diversifying its activities. After visiting the Monte Bondone hillclimb event near Trento in the late 1960s, he developed an interest in motorsport and in the engineering demands of competitive vehicles. In 1970 he moved the company into the light alloy sector, producing components for engines and motor vehicles. By 1972 he had established a dedicated alloy wheel business under the name Fondmetal, which would eventually grow into a well-regarded manufacturer of aftermarket wheels and OEM supplier to the automotive industry.
Rumi entered Formula One as a sponsor, backing fellow Italian Piercarlo Ghinzani. His ambitions grew beyond sponsorship, and in 1990 he purchased the struggling Osella team outright. He renamed the operation Fondmetal for the 1991 season, transforming it from a privateer entrant operating with Cosworth power into a team that sought a more competitive technical path.
Dissatisfied with the performance of the Fomet-1 chassis used in 1991, Rumi commissioned a completely new design from Sergio Rinland's Astauto studio. The resulting Fondmetal GR02, introduced partway through the 1992 season, earned praise from journalists and drew attention for its aerodynamic innovation. However, the cost of running the team exceeded Fondmetal's resources, and after the 1992 Italian Grand Prix Rumi took the decision to withdraw from competition. The team folded before the end of the season, though Fondmetal's wind tunnel remained available to other Formula One competitors as a commercial facility in the years that followed.
Rumi returned to the role of team owner in 1996, joining a consortium that acquired the Minardi Formula One team. By 1997 he had become the team's majority shareholder. His tenure at Minardi was shorter than his time with Fondmetal; at the end of 2000 he sold his shares to the Pan-American Sports Network, the organisation that sponsored Minardi driver Gastón Mazzacane. That group subsequently sold the team to Australian businessman Paul Stoddart.
Gabriele Rumi died of cancer on 21 May 2001 at the age of 61. Born in Palazzolo sull'Oglio in the Lombardy region of northern Italy, he had spent his entire adult life in industrial manufacturing and motorsport, and his two periods as a Formula One team owner — first building from scratch with Fondmetal, then stabilising and eventually departing from Minardi — reflected both his ambition and the persistent financial pressures that characterised the back half of the Formula One grid throughout the 1990s.