In the late 1940s, the French Army commissioned the major state arms factories at Tulle (MAT), St. Étienne (MAS), and Châtellerault (MAC) to produce a new 9×19mm submachine gun to replace the MAS-38, which had fallen out of favor due to its low-powered 7.65×20mm cartridge. Some of the features requested by the Army were a folding stock and a folding magazine.
St. Étienne developed their competitor, the MAS 48, initially in 1947. As per the Army's request, it featured a folding wooden stock and the magazine housing was hinged to allow the magazine to fold underneath the barrel when not in use. The MAS 48 was submitted to military trials but lost out to Tulle's design, the MAT-49.
Some variants were also developed in .30 Carbine for the French Army's carbine project, which was later scrapped due to lack of funding.
The MAS 48 was a blowback-operated submachine gun with an "L-shaped" bolt, consisting of a protruding bolt head and long bolt carrier which runs through the cocking tube located along the top of the barrel. It was initially designed with a lever-delayed blowback system but this feature was dropped after it was found to be unnecessary.
Rather than a conventional fire selector, the MAS 48 utilized a touch-sensitive trigger that gave single shots when pressed lightly and automatic fire when pulled back fully. The safety was located in the grip.