The PM-98 submachine gun was developed in Poland as an improved version of the PM-84P Glauberyt submachine gun. The PM-98 shares same internal design, but features redesigned polymer handguard and charging handle. The magazine release catch was relocated to the base of trigger guard to facilitate faster reloading, and therefore magazines are not interchangeable between PM-84P Glauberyt and PM-98 submachine guns. A semi-automatic version of the PM-98 is manufactured for police and civilian (where legal) markets as BRS-99, in carbine (with buttstock) or pistol (without buttstock) form.

The PM-98 submachine gun is a simple blowback operated weapon that fires from closed bolt. Submachine gun features internal hammer unit and a rate-of-fire reduction mechanism (which is absent in the PM-98S version). Gun can fire in single shots or in full automatic mode, thanks to the combined fire mode selector / safety switch, located on the left side of receiver. It also features a bolt hold-open mechanism, with bolt release lever located in front of the safety / selector lever, above the grip. The single charging handle is located on the left side of the gun (as opposed to the PM-84). The polymer forend is hollowed at the front to provide installation point for a tactical flashlight or a laser aiming module. The buttstock is retractable, with dual stamped steel struts. The rear sight is adjustable for zeroing and is set for 75 meters range.