The weapon's design is derived from the World War II era MG 42 that fired the 7.92×57mm Mauser round.

[8] The MG 3 was standardized in the late 1950s and adopted into service with the newly formed Bundeswehr, where it continues to serve to this day as a squad support weapon and a vehicle-mounted machine gun.

[9] At the end of World War II the original technical drawings and data for the 7.92×57mm Mauser chambered MG 42 were captured by the Soviets.

The MG 1A2 added new bolt-bounce preventing bolt catches to the action to resolve the ammunition ignition timing sensitivity of the preceding variants and was adapted to use both the standard German non-disintegrating Patronengurt DM1 ammunition belt and the American M13 disintegrating belt.

Compared to the MG 1A3, the MG 3 features an improved feeding mechanism with a belt retaining pawl to hold the belt up to the gun when the top cover plate is lifted, an added anti-aircraft sight and a new ammunition box.

The preceding non–MG 3 variant machine guns in the Bundeswehr inventory were gradually converted to the MG 3 standard.

The machine gun crew member responsible for a hot barrel change is issued protective asbestos gloves or a cloth to prevent burns to the hands.

The machine gun has an automatic-only trigger mechanism and a cross-bolt safety in the form of a button that is operated by the shooting hand (in its "safe" position the bolt release is disabled).

On MG 3 machine guns, two types of bolts are available, with standard weight (about 650 g (22.93 oz)) for the standard 1,000–1,200 rounds per minute cyclic rate of fire[17] and with extra weight (about 900 g (31.75 oz)) for a slower 800–950 rounds per minute cyclic rate of fire.

The rear wall of the drum is transparent and serves as a visual indicator for the amount of ammunition available.

For the light machine gun role the MG3 is equipped with a synthetic polymer stock and a folding bipod.

The MG 3 has a quick-change, chrome-lined barrel with four right-hand grooves and a rifling twist rate of 1 in 305 mm (1:12 in) and weighs 1.7 kg (3.7 lb).

Then, the breech end of the hot barrel swings out and can be removed by elevating or twisting the gun.

When the catch is rotated back, the barrel is locked and the machine gun can resume firing.

The machine gun crew member responsible for a hot barrel change is issued protective asbestos gloves to prevent getting burned.

Alternatively the MG3 can also be fed by disintegrating metal M13 link belts (designated DM60 by Germany) used by many NATO member states.

The feeding system is based on the direct push-through of the cartridge out of the belt link into the gun's chamber.

The Gurttrommel is not a true magazine but holds a curled 50-round belt preventing it from snagging, twisting and getting stuck during mobile assaults.

[19] In a stationary, heavy machine gun role the MG 3 is mounted on a buffered Feldlafette ("field tripod") that also features storage containers for accessories like the Zielfernrohr 4 × 24 periscope-style telescopic sight.

[14][15] A feature of the German World War II Lafette 42 tripod that was not carried over to the MG3 Feldlafette was the Tiefenfeuerautomat ("in-depth automatic fire").