The Mod.12 and 12s have been adopted by the Italian army, the Carabineri, and by some other military and police agencies around the world. The Beretta Model 12 submachine gun is blowback operated, selectively-fired weapon that fires from open bolt. The bolt is of telescoped design, and most of its weight is located in front of the breech face. Tubular receiver is made from steel stampings, with stamped steel trigger and magazine housing below.

Original PM 12 / Model 12 submachine guns featured separate manual safety and fire mode selector, both being made in the form of the cross-bolt buttons. Additionally, there was an automated grip safety below the trigger guard. On PM 12S submachine guns, manual safety and fire mode selector were united into one three-position lever, located above the left grip panel. Automated grip safety was retained. The furniture included polymer front grip and a side-folding metallic buttstock.