The 131 was the replacement for the successful Fiat 124, and available as a 2-door and 4-door saloon and 5-door estate. The 131 was given the Mirafiori name after the Turin suburb where the cars were produced. Naming the car in this way marked a break with the former Fiat convention, established in the 1960s, of naming their mainstream models only with a three digit number, and it set the pattern for Fiat to adopt Anglo-American style car naming practice, with carefully chosen names for subsequent new models. Initially, the 131 was offered with 1.3 L and 1.6 L single overhead camshaft engines. Revisions were made in 1978 and 1981, and all models were produced until production ceased in 1984.
In total, 1,513,800 units were produced in Italy.
Initially the 131 came with 1,297 cc or 1,585 cc straight-4 ohv engine. The first series was available with two body styles; saloon and estate Familiare. Station wagons were built by SEAT in Spain, but were labelled Fiats for all non-Spanish markets. There were two trim levels - the basic "131" and the better appointed "131 S" or "131 Special", which could be distinguished from the base model by its 4 circular headlamps, chrome window surrounds and different instrumentation. US market versions had an SOHC 1.8-litre four and were available with a GM three-speed automatic.
In 1976, 500 examples of Fiat 131 Abarth Rallye were built for homologation purposes. This car included many technical modifications such as 16-valve DOHC engine producing 140 PS (103 kW; 138 hp), Kugelfischer mechanical fuel injection and independent rear suspension. In race specifications, the engine produced around 215 PS (160 kW) in season 1977. Another special version was the nearly 5 metre long "131 Diplomatic" limousine version made in Salvatore Diomante's carrozzeria near Turin.
The 131 got a minor facelift in 1978. New DOHC, or "Twin Cam" (TC) engines arrived, and these models were badged as SuperMirafiori. The biggest change exterior-wise for the Series 2 was larger rectangular shaped front lights (quad round headlights in the US), new bumpers, new bigger rear lights and new interior trim including a chunky, single-spoked steering wheel.
Also in 1978, the 2-door sporting version Racing (Mirafiori Sport in the UK) with 115 PS (85 kW) twin cam engine, was launched. This car had four round headlights (the inner headlights being smaller than the outer ones, unlike any other Mirafiori model produced), different grille, spoilers and extended wheel arches, and a short-throw 5 speed gearbox. The Racing had top speed of 180 km/h (110 mph). Diesel engined versions also had four round headlights (equally sized), and a noticeable bump in the hood to accommodate the taller engine. The Familiare (estate) was renamed as Panorama.
The Series 2 was marketed in the United States as the Fiat Brava from mid-year 1978 with the same 1.8-litre four as had been used in the US-market 131, but before the year was over this was replaced by the 2 litre twin cam four also seen in the Spider. Initially, a better equipped Super Brava was also available, but the base model and "Super" tag were dropped for 1979. For 1980 a more powerful fuel-injected version was added (102 hp/76 kW) while the Estate version was dropped. For 1981 the EFI engine became standard equipment and the headlamps were changed for single rectangular units, but this was to be the last year for the Brava/131 in the US
The 131 was updated again in March 1981. By this time, the car was no longer offered in the USA. Production of the Racing/Sport versions ceased, although these were sold well into 1982. The same 2.0 TC (twin cam) engine went to the SuperMirafiori. The car was renamed 131 Super Brava in Australia. The car received a slightly updated interior (instruments, single-piece glovebox lid), whilst lower rubbing strips found their way onto all models up to CL specification. The SuperMirafiori received larger lower door cladding. Mechanically, Mirafiori versions now received overhead cam engines rather than pushrod versions; a new 1.4 litre engine and a revised 1.6 litre. Also new were the clutch and gearboxes, a tweaked suspension was also introduced and the gas tank increased in size by three litres, for a total 53 L (14.0 US gal; 11.7 imp gal) capacity.
In June 1981, a new sport version, the Volumetrico Abarth, was introduced to some markets, with a supercharged version of the familiar 2-litre twin-cam. This car, also known as the 2000 TC Compressore, was built in a small series and could reach 190 km/h (118 mph).
In 1983, the production of saloon version was discontinued, but the estate, now named 131 Maratea, remained in production with two engine choices (115 PS 2.0 TC and 72 PS 2.5 D) until 1985, when they were replaced with the Ritmo-based Regata Weekend. These last versions featured 4 round headlights and the by-now familiar 5-bar grille.