The 131 Abarth was derived from the Fiat 131 Mirafiori, a mid-size family saloon introduced at the 1974 Turin Motor Show. The standard road car used conventional front-engine, rear-wheel-drive architecture with MacPherson strut front suspension and a live rear axle. When Fiat sought to build a world-championship-calibre rally car from the platform, Abarth and Bertone were given strict instructions to stay as close as possible to the base model in appearance and parts selection.
Bertone took part-completed two-door bodyshells from the Mirafiori production line, fitted plastic front and rear mudguards, a plastic bonnet and bootlid, and modified the metal structure to accept a fully independent rear suspension. The finished shells were painted, trimmed, and delivered to Fiat's Rivalta plant where Abarth installed the competition mechanicals.
To satisfy Group 4 homologation requirements, Fiat built 400 road-legal examples. The street car used a dual-overhead-camshaft, four-valves-per-cylinder derivative of the standard twin-cam inline-four engine, fed by twin downdraught Weber 34 ADF carburettors. In this form it produced 140 PS at 6,400 rpm, with 172 Nm of torque at 3,600 rpm. The gearbox was the standard unit without synchromesh — regulations required competition cars to use the same synchromesh specification as the road cars — and the revised front bodywork improved brake-disc cooling significantly. The rear brakes were upgraded to discs in place of the standard drums.
For competition, the 131 Abarth received dry-sump lubrication and eventually Kugelfischer mechanical fuel injection. In race trim the engine developed up to 240 PS by 1980. The car retained rear-wheel drive throughout its WRC career, making it a demanding machine to drive fast but rewarding in the hands of skilled crews.
Between 1975 and 1977 the official works cars carried the Olio Fiat blue-and-yellow livery. From 1978 the team ran under Alitalia sponsorship and the cars appeared in the airline's distinctive red, white, and green colours.
Between 1976 and 1981 the Fiat 131 Abarth won 20 WRC events. The manufacturers' World Rally Championship went to Fiat in 1977, 1978, and 1980 — the 1979 title going to Ford's Escort RS1800 in the only season Fiat did not claim it during this stretch.
Markku Alen of Finland won the 1978 FIA Cup for Drivers behind the wheel of the 131 Abarth. Walter Röhrl of West Germany drove the car to the 1980 drivers' World Rally Championship, a season in which the combination of his precision on tarmac and the car's rear-wheel-drive handling rewarded consistent stage-winning pace.
Other notable drivers who scored WRC victories in the 131 Abarth included Sandro Munari, Timo Salonen, Attilio Bettega, and Michèle Mouton, demonstrating the breadth of talent the works team was able to attract and develop.
The 131 Abarth's direct predecessor was the 3.5-litre Group 5 Abarth SE 031, which won the 1975 Giro d'Italia automobilistico. In 1977, Abarth prepared three diesel-engined 131s with two-door, Series 1 bodyshells for the London-Sydney Marathon rally, entered by the French Esso Aseptogyl team. Two of these diesel cars finished, in 15th and 23rd place, validating the engine's durability ahead of the diesel variant's production launch.
In 1978, American actor James Brolin campaigned a 131 Abarth on a limited IMSA GT Championship schedule in the GTU category, the car carrying Anheuser-Busch Natural Light sponsorship.
The 131 Abarth stands as the last rear-wheel-drive car to win the WRC manufacturers' title before four-wheel-drive Audis and Group B regulations transformed the sport from 1982 onward. Its engineering philosophy — lightweight modifications to a production bodyshell, a highly developed naturally aspirated engine, and competitive suspension geometry achieved within homologation rules — defined the Group 4 formula at its most successful. The three manufacturers' titles it earned in a four-year span remain a benchmark for the pre-turbo era of world rallying.