The 250 S was developed as an evolution of the preceding Ferrari 225 S. It utilized a Tuboscocca tubular steel chassis, a trellis space frame design featuring small-diameter tubes and additional cross members. This chassis type, developed by Gilco and Gilberto Colombo, was intended to be lighter and more rigid than standard tubular frames. The 250 S retained the wheelbase and track dimensions of its predecessor.
The vehicle featured a closed berlinetta body designed by Giovanni Michelotti and constructed by Vignale. Its styling included two portholes in the front fenders and an external fuel filler cap mounted on the rear window. Following its debut at the Mille Miglia, the bonnet was updated with an air-scoop. The front windshield was equipped with three small wipers, one of which was positioned on the roof. The "ET" suffix in the chassis number stood for "Export-Tuboscocca."
The car was powered by a 3.0-litre Colombo V12 engine designed by chief engineer Aurelio Lampredi. The engine was based on the 225 S unit but featured a bore increased by 3 mm, resulting in internal measurements of 73 by 58.8 mm and a total displacement of 2,953.21 cc. This capacity was intended to maximize performance within "Sport 3.0" category regulations.
The engine utilized an SOHC, two-valve configuration with three Weber 36DCF carburettors. It featured a wet sump lubrication system, two coils serving a single spark plug per cylinder, and a compression ratio of 9:1. The power output was 230 PS (169 kW; 227 hp) at 7500 rpm. The drivetrain consisted of a single-plate clutch and a five-speed non-synchronised gearbox.
The front suspension was an independent setup using unequal-length wishbones and transverse leaf springs. The rear featured a live axle with semi-elliptical springs. Both the front and rear were equipped with hydraulic shock absorbers. Braking was provided by drum brakes at all four corners.
The 250 S made its competitive debut at the 1952 Mille Miglia, entered by Scuderia Ferrari for drivers Giovanni Bracco and Alfonso Rolfo. Despite competition from factory-entered Mercedes-Benz W194 300 SLs, Bracco and Rolfo overtook the leading Mercedes of Karl Kling on the Futa and Raticosa passes to win the race overall.
For the 1952 24 Hours of Le Mans, Scuderia Ferrari entered the 250 S in the "Sport 3.0" category for drivers Alberto Ascari and Luigi Villoresi. During the race, Ascari set the fastest lap with a time of 4min 40.5sec (an average speed of 173.16 km/h), nearly matching the fastest practice lap of the race-winning Mercedes team. However, the car was forced to retire due to a broken clutch.
Later in 1952, Luigi Villoresi drove the car to a third-place finish in the "Sport +2.0" class at the Circuito di Senigallia. The car achieved another major victory at the 12 Hours of Pescara (the Coppa Acerbo), where it was driven to first place by Giovanni Bracco and Paolo Marzotto. The 1952 season concluded with an entry in the Carrera Panamericana for Bracco and Gino Bronzoni, though the car failed to finish due to engine and clutch issues.
In 1953, the car was campaigned at the Giro di Sicilia by Franco Cornacchia and Gino Bronzoni, but they retired with a broken differential.
The 1952 Mille Miglia remains the defining victory for the 250 S, as it successfully defended Ferrari's dominance in the Italian road marathon against the new Mercedes-Benz works team. While the 250 S proved its speed at Le Mans by setting the fastest lap, the mechanical failures there and at the Carrera Panamericana highlighted the reliability challenges faced during its primary factory campaign.
In 1953, the 250 S was sold to Argentinian driver Roberto Bonomi. Under Bonomi's ownership, the car was entered in the Targa Florio, where he finished eighth overall and sixth in the "S 3.0" class. The car also appeared at the GP Monza, entered by Scuderia Guastalla, where it finished eighth. Bonomi later entered the Coppa d'Oro delle Dolomiti but did not achieve a significant result.
The final recorded competitive appearance for the 250 S was the 1954 Supercortemaggiore at Monza. Entered by Scuderia Guastalla and driven by the duo of Musitelli and Pezzoli, the car failed to finish the race.
The 250 S was the first Ferrari to utilize the 3.0-litre displacement that would define the 250 series for over a decade. The technical data and racing performance gathered from this single prototype led directly to the development of the Ferrari 250 MM, the first series-produced race car in the 250 lineage.