- Panzer III Ausf. A - Prototype; only 8 armed and saw service in Poland. Armed with 3.7 cm KwK 36 L/46.5 main gun, 250 PS HL 108 engine.
- Panzer III Ausf. B - Prototype; some saw service in Poland.
- Panzer III Ausf. C - Prototype; some saw service in Poland.
- Panzer III Ausf. D - Prototype; some saw service in Poland and Norway. Armour upgraded to 30 mm front, side and back.
- Panzer III Ausf. E - Suspension redesigned, switching from leaf-springs to torsion-bars, now using 6 larger roadwheels per side. 300 PS HL 120 engine.
- Panzer III Ausf. F - improved Ausf. E, first mass-production version, late production armed with 5 cm KwK 38 L/42 main gun.
- Panzer III Ausf. G - More armour on gun mantlet. Armed with 3.7 cm KwK 36 L/46.5 (later 5 cm KwK 38 L/42) gun.
- Panzer III Ausf. H - 5 cm KwK 38 L/42 as standard gun. Bolt-on armour added to front and rear hull (30 mm base + 30 mm plates).
- Panzer III Ausf. I - Variant mentioned in Allied intelligence reports but not an actual existing vehicle. Possible confusion with Ausf. J.
- Panzer III Ausf. J - Hull and turret front armour increased to solid 50 mm plate. Some were produced with 5 cm KwK 39 L/60 gun and later redesignated Ausf. L.
- Panzer III Ausf. K - Panzerbefehlswagen command tank variant with a modified turret. Carried actual main armament rather than a dummy gun as found on other Panzer III command versions.
- Panzer III Ausf. L - Redesignated Aus. J equipped with long 5 cm gun, 20 mm stand-off armour plates on hull and turret front
- Panzer III Ausf. M - Minor modifications of the ausf. L such as deep-wading exhaust and Schürzen side-armour panels.
- Panzer III Ausf. N - Infantry support tank, armed with a short-barrelled 7.5 cm KwK 37 L/24 gun.
- Panzerbeobachtungswagen III - Forward artillery observer tank. 262 converted from older Panzer III Ausf. E to H.
- Bergepanzer III - In 1944, 176 Panzer IIIs were converted to armoured recovery vehicles. Mostly issued to formations with Tiger I tanks.
- Flammpanzer III Ausf. M / Panzer III (Fl) - Flamethrower tank. 100 built on new Ausf. M chassis.
- Minenräumer III - Mineclearing vehicle based on a Panzer III chassis with a very highly raised suspension. (Prototype only.)
- Panzerbefehlswagen III - Command tank with long-range radios. Ausf. D, E and H: dummy main gun; Ausf. J and K: armed with 5 cm gun.
- Sturm-Infanteriegeschütz 33B - A close-support assault gun. Armed with a 15 cm sIG 33, 24 built. 12 used and lost in Stalingrad.
- Sturmgeschütz III - Assault gun/tank destroyer armed with a 75-millimetre (2.95 in) StuK.
- The Soviet SU-76i self-propelled gun was based on the chassis of captured German Panzer III and StuG III. About 201 of these vehicles, many captured in the battle of Stalingrad, were converted at Factory No. 37 in 1943 for Red Army service by removing the turret, constructing a fixed casemate, and installing a 76.2-millimetre (3.00 in) S-1 gun (cheaper version of the F-34) in a limited-traverse mount. The armour was 35 millimetres (1.38 in) thick on the casemate front, 50 millimetres (1.97 in) in the hull front, and 30 millimetres (1.18 in) on the hull side. It was issued to tank and self-propelled gun units starting in autumn 1943, and withdrawn to training use in early 1944. Two SU-76i survive: one on a monument in the Ukrainian town of Sarny and a second on display in a museum on Poklonnaya Hill in Moscow. It should not be confused with the Soviet SU-76 series.
- Tauchpanzer III - Some tanks were converted to amphibious tanks for Operation Sea Lion. Unusually, they were designed to be able to stay underwater rather than to float. The idea was that they would be launched near to the invasion shore and then drive to dry land on the sea bottom. The tank was waterproofed, the exhaust was fitted with a one-way valve and air intake was through a hose.