The MP28.II was developed at the C.G. Haenel plant in Suhl under the direction of Hugo Schmeisser. It was based on the SIG M1920, a Swiss-made MP18 variant. Initially the gun was blocked from production in Germany due to the Treaty of Versailles, so Haenel outsourced production to Pieper in Belgium, but by the mid-1930s, the new Nazi regime disregarded the Treaty and began an extensive re-armament campaign, allowing the MP28.II to undergo production domestically at Haenel.
It was offered for both the domestic and export market, and saw considerable international sales. It was available in a variety of chamberings, predominantly 9×19mm, but also 7.65×21mm, 7.63×25mm, and .45 ACP, among others.
Belgium adopted the MP28.II in 1934, and it also saw sales to Portugal and various South American countries. During the Spanish Civil War, the Nazi government sold large quantities of MP28s to the Nationalist rebels. The gun was known as La Naranjero in Spain and was extensively copied. During World War II, the MP28.II was issued to the Waffen-SS, but quickly fell out of favor due to its high production costs compared to the MP 40. It was never formally adopted by the Wehrmacht. Production ended in 1940.
The MP28.II was a basic blowback-operated submachine gun that was internally and externally derived from the earlier MP18.I. The main improvement over the MP18.I was the inclusion of a fire selector device in the form of a cross-bolt switch above the trigger group, which could give single shots or fully-automatic fire. The narrow recoil spring and guide rod of the MP18.I was replaced by a wide diameter spring.
The MP28.II did not accept the canted "snail" drum magazines of the MP18.I, but instead used twin-column straight box magazines of 32 rounds. To facilitate for this, the magazine feed was redesigned. The fixed rear sight of the MP18.I was also replaced by an adjustable tangent sight that graduated up to 1,094 yards.