The 300 SL traces its lineage to the Mercedes-Benz W194 endurance racer developed by Daimler-Benz in 1951. The W194 used a 3-litre inline-six M186 engine shared with the company flagship 300 "Adenauer" saloon and the two-seat 300 S grand tourer. Although the engine's 175 hp output was less than competing Ferraris and Jaguars, the W194's low weight and low aerodynamic drag kept it competitive. Mercedes developed an evolution for the 1953 season fitted with mechanical direct fuel-injection and a magnesium-alloy body, but ultimately decided not to race it and redirected resources toward a Formula One programme beginning in 1954.
The production 300 SL originated from a proposal by Max Hoffman, Mercedes-Benz's United States importer, made at a 1953 directors' meeting in Stuttgart. General director Fritz Konecke agreed to Hoffman's order for 1,000 cars to underwrite the production run. The car debuted at the February 1954 New York International Auto Show rather than at the Frankfurt or Geneva shows where Mercedes models normally appeared, and production started at the Sindelfingen plant later that year. A companion model, the 190 SL roadster, was announced at the same time following a separate Hoffman order.
The 300 SL's chassis was a chrome-molybdenum steel tubular frame designed by chief engineer Rudolf Uhlenhaut, assembled from thin straight tubes in triangulated sections and weighing just 82 kilograms while providing exceptional rigidity. The frame was so deep along the cockpit that conventional hinged doors were impractical; the solution — already used on the W194 race car — was an upward-opening gullwing door, which became the coupé's defining feature and gave it its popular nickname.
The M198 power unit is a water-cooled 3.0-litre overhead-camshaft straight-six tilted 50 degrees toward the driver's side to achieve a low bonnet line. A Bosch mechanical direct fuel-injection system raised output to 240 hp (179 kW) at 6,100 rpm, compared with 175 hp in the carburetted W194. Dry-sump lubrication ensured consistent oiling under high-speed cornering. A more powerful variant with a sports camshaft and 9.5:1 compression was available for the coupé at no extra charge. With the lowest offered final-drive ratio of 1:3.25, maximum speed reached 263 km/h (163 mph), making the 300 SL the fastest production car of its time.
Four-wheel independent suspension was adapted from the W186 "Adenauer," using unequal-length double wishbones with coil springs at the front and a low-pivot swing axle with radius arms at the rear. The rear geometry's extreme camber changes at high speed or on poor surfaces could make cornering demanding, an issue addressed in the later roadster by switching to a high-pivot arrangement. Front drum brakes of 1,470 cm² were shared with the Mercedes 300 S; disc brakes replaced them all round from March 1961.
The coupé was priced at DM 29,000 in Germany and $6,820 in the United States. An all-aluminium body option was available but only 29 such cars were produced.
The 300 SL made its competitive debut at the 1952 Mille Miglia, where Karl Kling finished second to Giovanni Bracco's Ferrari by four minutes and 32 seconds, with Rudolf Caracciola placing fourth. A fortnight later at Bern, Kling, Hermann Lang, and Fritz Riess finished first, second, and third after the leading Ferrari retired. At the 1952 24 Hours of Le Mans three new cars were entered; Lang and Riess won with an average speed of 155.574 km/h, and Theo Helfrich and Helmut Niedermayr placed second. Later that season at the Nürburgring the roof was removed to create an open variant, and Lang again won, with Kling and Riess second and third.
The team contested the third Carrera Panamericana in Mexico with cars modified to 3.1-litre displacement to place them in a competition class. Kling and co-driver Hans Klenk won, with Lang and Erwin Grupp second; a potential 1-2-3 was denied when American John Fitch was disqualified for receiving mechanical assistance on the penultimate day. Kling struck a buzzard during the early stages at approximately 135 mph.
In 1955, Werner Engel won the European Rally Championship in a 300 SL, while John Fitch won his class at the Mille Miglia in a production coupé. Olivier Gendebien won the Liège–Rome–Liège rally in 1955, and Willy Mairesse repeated the feat in 1956. The 300 SL claimed the Sports Car Club of America Class D championship for three consecutive seasons from 1955 to 1957.
For 1957 a lightened roadster variant — informally known as the 300 SLS (Super Light Special) — was built to compete in the SCCA D Modified class. The O'Shea-Tilp team's car featured drilled front coil-spring mounts, a welded sheet-aluminium inlet manifold, twin exhaust outlets, a roll bar, and no bumpers, reducing weight from 1,420 kg to 1,040 kg with engine output increased to 235 hp. It won the 1957 Class D Sports championship with triple the points of its nearest competitor, Carroll Shelby's Maserati.
When coupé sales began declining in mid-1956, Mercedes-Benz developed a convertible version targeting the California market. A prototype was shown at the Geneva Motor Show in March 1957 and production converted from May that year. The tubular frame was redesigned to lower the sills and accommodate conventional door hinges, and the rear swing axle received a higher-pivot geometry that substantially improved handling. Despite aluminium panelling for the bonnet, boot lid, door skins, sills, floors, and bulkhead, the roadster weighed 35 kg more than the coupé at 1,330 kg.
A folding soft top was standard from launch; a weatherproof hardtop option was introduced in September 1958 and proved so popular that Mercedes offered the roadster without the soft top for a DM 750 discount. The roadster's price was DM 32,500 in Germany and $10,950 in the United States — more than 70 percent more expensive than the coupé in dollar terms. Production ended in February 1963 after 1,858 roadsters, the last Mercedes-Benz car built on a separate frame.
The 300 SL established the SL family name. A companion 190 SL was introduced in 1955 and succeeded by the 230 SL in 1963, a line that continued through 280 SL variants to 1971. Subsequent SL generations included the R107 (1971–1989) and R129 (1989–2001). The gullwing format was revived in 2009 with the V8 SLS AMG, regarded as the spiritual successor to the original coupé, produced until 2014 when it was replaced by the AMG GT. Mercedes-Benz obtained court protection for the 300 SL's design against faithful reproductions. Gull Wing Group International, founded in 1961, continues to support owners worldwide.