The 1908 race was run under a new formula that departed significantly from the 1906 regulations. There was no fuel consumption limit, but cars were required to have a minimum weight of 1,100 kilograms and a maximum cylinder bore of 155 millimetres. This approach — controlling power indirectly through bore dimensions rather than fuel economy — reflected ongoing attempts by governing bodies to limit the performance of the increasingly powerful racing cars of the era.
The formula differed from the regulations in place for the American Vanderbilt Cup series, which had the practical effect of discouraging American manufacturers from entering. Lewis Strang drove the single American entrant, a Thomas Flyer. D. Napier and Son entered cars but were disqualified from the race before it started due to their use of Rudge-Whitworth centre-locking hubs, which the organisers judged to be unsafe.
Christian Lautenschlager's Mercedes dominated the race from start to finish. He won with an average speed of 69.045 mph (111.117 km/h) over the Dieppe circuit, finishing nearly nine minutes ahead of Victor Hémery in a Benz. Otto Salzer, also in a Mercedes, set the fastest lap of the race at an average speed of over 78 mph (126 km/h).
The race was notable for tragic reasons. Henri Cissac, competing in the race, suffered a tyre failure that caused his car to roll. Both Cissac and his riding mechanic Jules Schaube were killed in the accident. This was the first fatal accident in the history of Grand Prix motor racing, and it underscored the dangers that had already caused the cancellation of the 1903 Paris–Madrid race and led to ongoing debate about the safety of motor racing on public roads.
The 1908 Grand Prix confirmed that Mercedes and the German automobile industry had arrived as a serious competitive force in Grand Prix racing, two years after the French-dominated 1906 event. Lautenschlager's victory — achieved by a driver who had not been among the pre-race favourites — highlighted the improved reliability and speed of the German cars under the new formula.
The race at Dieppe was the second edition of the revived Grand Prix de l'Automobile Club de France; the 1907 race had also been held at Dieppe, won by Felice Nazzaro for FIAT. After 1908, the Grand Prix was not held again until 1912, reflecting both the commercial pressures on the French automobile industry and ongoing arguments about the appropriate formula for Grand Prix racing.
The first fatality in Grand Prix history at the 1908 race added urgency to discussions about race safety that had been building since the Paris–Madrid disaster of 1903. The presence of riding mechanics — required to accompany drivers in all Grand Prix cars of this era — meant that accidents claimed not one but two lives each time a car rolled or crashed heavily, a compounded risk that would influence subsequent regulatory changes.