The P-3AT is a semi-automatic, locked breech pistol, chambered for the .380 Auto cartridge. It has been developed from the highly successful P-32 pistol with negligible increase in weight and size. The slidestop has been eliminated and the magazine capacity reduced to 6 rounds due to the larger cartridge. The firing mechanism is double action only. The magazine has a 6 round capacity. The KEL-TEC P-3AT is the lightest .380 Auto pistol ever made. Thanks to its locking dynamics and superior ergonometry, perceived recoil and practical accuracy are comparable to much larger guns. The P-3AT is mainly intended for plainclothes police officers as a secondary weapon, or for concealed carry by licensed citizens. The small grip size and light trigger pull make the P-3AT ideal for female shooters.

The P-3AT has five main component groups: barrel, slide, firing mechanism, grip, and magazine. The barrel is made of SAE 4140 ordnance steel, heat treated to 48 HRC. The slide is also 4140 steel, and contains the firing pin and the extractor. The rectangular frame is machined from solid 7075-T6 aluminum and houses the firing mechanism. The trigger connects via a transfer bar to the hammer. The hammer is driven by a novel free floating extension spring. The light weight firing pin transmits the energy of the hammer to ignite the primer. After firing, the hammer block holds the hammer away from the firing pin, providing a mechanical safety.