The season was defined by a series of fatalities. Two drivers died during the Indianapolis 500: Manny Ayulo and reigning Indy winner Bill Vukovich. At the non-championship Pau Grand Prix, Italian Mario Alborghetti was killed. Most significantly, Alberto Ascari — double World Champion of 1952 and 1953 — was killed while testing a Ferrari 750 Monza at Monza, just days after his dramatic escape from the Monaco harbour.
The greatest tragedy of all came at the 24 Hours of Le Mans on 11 June, when ex-Formula One driver Pierre Levegh crashed into the spectator enclosure, killing 83 people. The disaster prompted the cancellation of four remaining Grands Prix — the French, German, Swiss, and Spanish rounds. Motor racing was banned entirely in Switzerland until the 2018 Zurich ePrix.
Stirling Moss joined Mercedes alongside Fangio, having driven for Maserati the previous year. Jean Behra moved from Gordini to Maserati. Vanwall signed Mike Hawthorn from Ferrari, which allowed Peter Collins to join Owen Racing Organisation. Lancia entered the season with full ambitions, fielding Alberto Ascari, Luigi Villoresi, and Eugenio Castellotti with their D50 cars. After Ascari's death and Lancia's financial collapse, the team handed all assets to Enzo Ferrari.
The opening round in Buenos Aires was run in extreme heat of 52 degrees Celsius. Multiple drivers exchanged cars during the race as heat and mechanical failures took their toll. Fangio was among the few classified drivers not to have changed cars, won the race, and immediately led the championship.
The Monaco Grand Prix returned to the calendar for the first time since 1952 and was accorded the honorary title of European Grand Prix. Fangio led initially but retired with a broken transmission. On lap 81, Ascari — unexpectedly in the lead — crashed coming out of the chicane and plunged into Monaco harbour. He was rescued with minor injuries. With both leaders out, Maurice Trintignant took an unlikely win for Ferrari, the first of his career.
Four days after Monaco, Ascari was killed at Monza in a testing accident. Lancia halted operations and eventually transferred all assets and cars to Ferrari.
Mercedes asserted dominance in the remaining European rounds. Fangio and Moss finished one-two in Belgium, then one-two again in the Netherlands — the first podium since the 1950 French Grand Prix not featuring a Ferrari-powered engine. At the British Grand Prix at Aintree, Moss scored his first career pole position and outpaced Fangio to win in front of his home crowd, Fangio hanging back on the final lap to allow his British teammate the moment.
The Le Mans disaster triggered the cancellation of France, Germany, Switzerland, and Spain, leaving just one more race.
At Monza, the banking was used for the first time and the Lancia cars were withdrawn as a precaution after Farina's tyre failure in practice. Fangio and Taruffi finished one-two for Mercedes, with Moss retiring. It was the final championship race for Mercedes-Benz until their 2010 return.
Juan Manuel Fangio finished with 40 points, winning the title ahead of Stirling Moss on 23 and Eugenio Castellotti on 12. Mercedes withdrew from all motorsport after the season.
Ascari's plunge into Monaco harbour and his subsequent death four days later at Monza remain two of the most haunting episodes in early Formula One history. His escape from the water was almost miraculous; the testing accident that killed him days later, in a car he was driving as a favour, added to the season's grim character.
Moss's win at Aintree — the first British driver to win a Formula One World Championship race on home soil in the modern era — drew enormous public attention and signalled the coming British invasion of the sport.
The 1955 season stands as the most tragically curtailed in Formula One history, tied with 1950 for the fewest World Championship races held in a year. The Le Mans disaster's shadow altered the trajectory of European motor racing regulation and caused permanent changes to circuit safety standards. Mercedes-Benz's withdrawal, effective immediately after Monza, ended the most dominant technical campaign the sport had yet seen, leaving the 1956 season wide open for the Italian constructors and their new rival, Vanwall.