The 1955 Formula One season was dominated by the Mercedes-Benz W196, with Juan Manuel Fangio, Stirling Moss, Hans Herrmann, and Karl Kling deployed across the team's campaign. The Monaco race had not been held continuously — it was absent from the calendar between 1938 and 1954 except for 1948, 1950, and 1952. Going into Monaco, the Silver Arrows were in commanding form, Moss having won the Mille Miglia weeks earlier, beating Fangio by half an hour. Hans Herrmann crashed near the harbour during Monaco practice and suffered injuries that kept him out for the rest of the season; André Simon took his grid slot. Karl Kling, who had crashed near Rome at the Mille Miglia and broken ribs, was also absent.
Fangio and Moss ran first and second in their Mercedes, trailed by Alberto Ascari in the Lancia D50 and Eugenio Castellotti in the second Lancia. At the halfway point Fangio retired with transmission trouble, handing the lead to Moss. Almost a full lap clear of the field, Moss appeared certain to win until his engine failed on lap 80.
The new race leader was Ascari. Driving car number 26 — the same number his father Antonio Ascari had carried when killed at the 1925 French Grand Prix — Alberto Ascari miscalculated the chicane exiting the tunnel. His Lancia plunged through the barriers and into Monaco harbour. Ascari was pulled from the water and spent the night in hospital. His car was later craned from a depth of 25 feet.
Maurice Trintignant, unheralded in the underpowered Ferrari 625, inherited the lead and held it to the finish. Eugenio Castellotti completed the podium for Lancia in second, with the Maserati pairing of Jean Behra and Cesare Perdisa sharing third place — Behra driving 42 laps, Perdisa driving 57. Piero Taruffi and Paul Frère also shared a car to finish in the points.
The race marked Cesare Perdisa's Formula One debut; he shared the third-place drive with Behra and collected a podium on his first appearance. It was also the only Grand Prix start for Ted Whiteaway, who failed to qualify. Louis Chiron's entry made him the oldest driver to start a Formula One Grand Prix at 55 years and 292 days old. Fangio broke the Monaco lap record during practice, lapping in 1:41.1 in the Mercedes W196 — surpassing the mark set in 1937 by Rudolf Caracciola in a 5.6-litre Mercedes W125.
Alberto Ascari's harbour crash was the last Grand Prix appearance of his life. Four days later, on 26 May 1955, he was killed at Monza while testing a Ferrari sports car. Post-accident analysis suggested the probable cause was an improperly sized tyre — 7.00x16 rather than the correct 6.50x16 — combined with an imperfect track surface, though no definitive explanation was ever established. Some investigators also noted the possibility of undetected injuries from the Monaco crash.
The 1955 season would end in further tragedy. Several months after Monaco, the 1955 24 Hours of Le Mans produced the worst accident in motor racing history, involving a Mercedes-Benz 300 SLR.
Trintignant's victory was the first Formula One win for a French driver and the first for Englebert tyres. It remained one of the most celebrated upset results in Monaco Grand Prix history, built on the collapse of every faster car in the field.