The selection of weapons provided in Grand Theft Auto III consists of firearms and explosives, with the addition of two forms of mêlée attacks (hand to hand combat and baseball bat).
The weapons themselves are largely similar to the selection of weapons from GTA1 and GTA2, such as the pistol, the machine gun (which has been expanded to include an Micro Uzi submachine gun, an AK-47 assault rifle and an M-16 assault rifle in GTA III), the rocket launcher and the flamethrower from GTA1, and the shotgun and thrown weapons (Molotov cocktails and grenades) from GTA2. The weapons weren't categorised, so a player could have all weapons at the same time.
The porting of the GTA III into a three dimensional environment also allowed for the inclusion of the sniper rifle and first-person aiming using the assault rifle and rocket launcher. In addition, it becomes possible in the game to perform drive-by shooting using the Uzi. The inclusion of magazine-based weapons also introduces the need to reload weapons after a magazine of ammunition is depleted. Additionally, wielding certain weapons would now restrict movement of the player. Weapons may be purchased from local firearms dealers and businesses, retrieved for free from certain dead gang members, mission-specific characters and law enforcers, or picked up in certain spots in the city.
The console versions of the game allowed the player to auto-aim with the push of a button, holding human targets at gun point using most firearms, with the exception of first person aiming for the sniper rifle, M-16 and rocket launcher, which are controlled by the analog stick as the player presses the same autoaim button. Because the PC version allows the player to aim targets with a mouse, the autoaim system was removed. This control difference is also seen in the console and PC ports of Vice City and San Andreas.
- Slot 1: Hand
- Slot 2: Melee Weapons
- Slot 3: Pistols
- Colt .45
- Slot 4: Shotguns
- Slot 5: Submachine guns
- Slot 6: Assault Rifles
- Slot 7: Assault Rifles (Heavy)
- Slot 8: Sniper
- Bolt Action Sniper Rifle
- Slot 9: Rocket Launchers
- LAW (Light Anti-tank Weapon)
- Slot 10: Incendiary Firearms
- Flamethrower
- Slot 11: Incendiary Projectiles
- Molotov Cocktail
- Slot 12: Fragment Projectiles
- Grenades
- Slot 13: Special
- Remote Detonator (Only Available if equipped with car-bomb from 8ball's in Shorside Vale)