Alfa Romeo entered 1951 defending their dominance with the 159 development of their pre-war supercharged design, now producing around 425 horsepower. However, Ferrari had developed their naturally aspirated 4.5-litre 375, a chassis that could exploit the Alfa's critical weakness: fuel consumption so extreme that both Fangio and Farina typically had to stop twice per race to refuel. Ferrari's cars could often run longer stints, neutralising Alfa's raw pace advantage during pitstop cycles.
Several significant changes affected the season. The Monaco Grand Prix was dropped from the calendar due to budgetary concerns. The German Grand Prix appeared for the first time since 1939, West Germany having been banned from international sporting competition until 1951. Spain was included for the first time as a World Championship round. The BRM team made their championship debut at the British Grand Prix with their complex V16-powered car, managing only one appearance before withdrawing.
The season opened in Switzerland at the Bremgarten Circuit, where Fangio converted pole position into victory. The Belgian Grand Prix at Spa-Francorchamps saw Farina win, with Ferrari's Alberto Ascari and Luigi Villoresi completing the podium.
The French Grand Prix at Reims-Gueux, awarded the honorary European Grand Prix designation for 1951, proved one of the most dramatic races of the season. The high-speed triangular circuit, made up of long straights and slow angular corners, suited both the Alfas and the powerful Ferraris. José Froilán González drove a stunning race for Ferrari, challenging hard before handing his car to Ascari during pitstops, while Fangio ultimately won after Fagioli was ordered to surrender his healthy car — an act that so enraged the veteran Italian that he retired from racing immediately afterward. The French Grand Prix also holds the record as the longest racing distance ever completed in a Grand Prix, at 600 kilometres.
The British Grand Prix at Silverstone marked a historic turning point. González, driving a Ferrari, defeated Fangio and Farina by exploiting the Alfa's fuel consumption disadvantage. The cars had to stop twice to refuel while González needed only one stop, and he crossed the line to give Ferrari their first ever World Championship Grand Prix victory. It was also the first time Enzo Ferrari's own construction had won a Grand Prix.
At the German Grand Prix on the Nürburgring Nordschleife, Ascari won his first championship Formula One race, benefiting from overheating problems afflicting the Alfas. Ferrari won again in Italy at Monza, with Ascari taking victory and keeping the championship alive heading into the Spanish finale.
The first ever Formula One Spanish Grand Prix, held on the Pedralbes street circuit in Barcelona, decided the title. Ferrari fielded a four-car team but their choice of smaller wheels led to rapid tyre degradation that cost them the race. Fangio drove away to victory, with González second and Farina third. The result gave Fangio his first of an eventual five World Championships, and ended Alfa Romeo's winning run. Alfa Romeo withdrew from Formula One at the end of the season, unable to fund a competitive new car for the regulatory changes coming in 1952.
Fangio won the championship with 31 points, Ascari finished second with 25, and Farina third with 19. Points were awarded on a 8-6-4-3-2 scale with a bonus point for fastest lap, with only the best four results from eight rounds counting toward the title.
The 1951 season represented a transitional moment in Formula One history. Alfa Romeo's retirement ended the era of the pre-war supercharged designs, and Ferrari's three race wins established them as the benchmark constructor going forward. Fangio's first title began a run of championship success that would make him the dominant figure of 1950s Formula One. The season also demonstrated that the naturally aspirated 4.5-litre formula could challenge the supercharged 1.5-litre cars when team strategy — particularly around fuel stops — was executed correctly.