The 300S emerged from Maserati's ambition to contest the World Sportscar Championship with a car closely related to its Formula One hardware. The project allowed the factory to leverage existing engineering rather than developing an entirely new platform, giving the 300S a technical lineage that connected sportscar and single-seater racing at Maserati during the mid-1950s.
The 3.0-litre straight-six engine was derived directly from the Maserati 250F's Formula One unit. Engineer Vittorio Bellentani lengthened the stroke to raise displacement from 2.5 litres to approximately 3.0 litres. FIA regulations for the World Sportscar Championship required competitors to use road-car fuel rather than exotic racing blends, so the compression ratio was reduced from 12:1 to 9.5:1. In this configuration the engine produced approximately 245 bhp at 6,200 rpm.
Induction was handled by three Weber carburettors — initially 42DCO3 units, later upgraded to 45DCO3 items. Unlike the 250F, the 300S incorporated a De Dion type rear axle, a transverse four-speed gearbox, and twin chain-driven camshafts. An attempt by engineer Giulio Alfieri to fit fuel injection was ultimately abandoned during development.
The 300S used a trellis frame structure in place of the tubular chassis employed on the 250F. The aluminium bodywork was crafted by coachbuilder Medardo Fantuzzi. Braking was entrusted to the same precisely machined alloy drum brakes with extensive finning as those used on the 250F, while the suspension geometry was carried over from the single-seater but reinforced to cope with the more demanding surfaces and longer distances of sportscar events.
The 300S's first season in 1955 was troubled by mechanical failures and development problems that prevented consistent results. The car found better form in 1956, winning at the Nürburgring and finishing second overall in the World Sportscar Championship standings, placed behind the more powerful Maserati 450S and ahead of the Maserati 350S in the marque's internal hierarchy.
Following the catastrophic accident at Guidizzolo during the 1957 Mille Miglia — an accident that effectively ended Maserati's works sportscar effort — the remaining unsold examples of the 300S were transferred to customers in the United States. One chassis was developed further using a new V12 engine, a conversion that formed the basis of the Maserati 350S.
The 300S has remained a presence in historic motorsport. Guitarist Mark Knopfler, formerly of Dire Straits, is a long-term owner of one example and has raced it in historic competitions. He also referenced the car in the song Red Staggerwing on his 2006 album All the Roadrunning.
The 300S represents Maserati's most coherent attempt to bridge its Formula One and sportscar programmes during the golden era of Italian racing. Its reliance on proven 250F architecture gave it a competitive foundation, while its results — particularly in 1956 — demonstrated that a production run of only twenty-six cars could still mount a serious challenge at the highest level of endurance racing.