The IAR-80 quickly proved superior to the He-112 on almost every aspect, excepting the armament ( the German plane was armed with two 20 mm canons and two machine guns, while the production version of the IAR-80 was planned to have six FN 7.92 mm machine guns mounted in the inner portion of the wings ). In December 1939, the IAR-80 was chosen by ARR as their new fighter. On the 18th of December 1939 an order for 100 IAR-80's was placed and production was supposed to start immediately, but unfortunately, after the German invasion of the west, the deliveries of FN machine guns ( remember that these were made in Belgium ) were stopped. Since Romania couldn't produce machine guns suitable for use in fighters, the production had to be put on hold. Only in November 1940, after Romania had clearly joined the Axis, did the Germans resumed deliveries, so it was January 1941 when the first IAR-80 left the factory.

20 IAR-80's were delivered by February, and were well received by the pilots of the 8th Fighter Group, the very first unit which received the IAR-80, with the mention that the aircraft was considered somewhat underpowered and seriously lacking firepower. Because there were still not enough FN machine guns, each plane got only 4 machine guns instead of 6, as it was planned initially. From the IAR-80 with serial number 21 to 50, the planes were fitted with the IAR K14 III C36 air-cooled, 14 cylinder double-row, radial engine, which could produce 960 HP.

By April 1941, FN machine guns were finally available in sufficient numbers, so it was decided to mount six of them on each aircraft in order increase firepower, starting from the 51st one. Additional modifications included the installing the more powerful IAR K14 C32 1000A engine ( once again it was a 14 cylinder, double row, air-cooled, radial engine ) which would equip all versions of IAR-80's and 81's from now on, as well as windscreen made out of armored glass, an armor plate behind the pilot and a new Goerz gunsight.

This version was designated as IAR-80A and it was a clear improvement over its predecessor, although top speed had dropped to 506 km/h because of the added weight of armor and armament. The new engine however generated a lot of vibrations, so the fuselage had to reinforced by using a duralumin "ring" mounted internally, just behind the cockpit Most of the early IAR-80A's were built using this method, until the fuselage could be strenthegned enough to cope with the engine vibrations. Production begun in April 1941, with some 90 IAR-80A's being built. On the 22nd of June 1941, when operation Barbarossa kicked off, the 8th Fighter Group was equiped with IAR-80's and IAR-80A's. The plane proved to be superior to anything the VVS had at the moment, enabling the IAR-80 pilots to score over 100 confirmed kills by October 1941 for the loss of just 21 IAR-80's. Most of the victories had been achieved by the men of the 8th group, which had shot down 75 confirmed enemy planes and destroyed 10 more on the ground. The group's finest moment was on the 7th of September, when they claimed 9 Soviet I-16 fighters shot down for no losses.

Production ramped up in the closing months of 1941, allowing the ARR to issue IAR-80A's to the 3rd, 8th ( where they replaced all the earlier IAR-80 models ) and 9th Fighter Groups. At that moment, the IAR-80's made up the bulk of ARR's fighter strength.

By the time the mass-production of the IAR-80A was underway, combat experience on the east front had demonstrated that the aircraft still lacked firepower, even with six machine guns. But there was virtually no other available armament except for what the IAR had already received. So, engineers decided to re-arm the plane with two 13.2 mm FN machine guns taken from Savoia-Marchetti SM 79 bombers. The wings were enlarged to fit the new armament and new radio gear was installed as well, creating the new version of the IAR : the IAR-80B. It entered production in June 1942 and eventually 50 IAR-80B's were produced until September 1942, when it was replaced by another version.

The IAR-80B's ( plus the existing A models ) and IAR-81's saw action in the Stalingrad area with the 6th and 8th Fighter Groups from September to late December 1942. By this stage, the IAR-80 was still equal or somewhat superior to most Soviet fighters, but the limitations of their K14 engines were beginning to show. Nevertheless, Romanian pilots continued to fly them with skill and courage, claiming 45 more VVS airplanes for the loss of 29 IAR-80's ( of which just 11 were actually shot down, the rest were lost in accidents or had to be abandoned when the Red Army threatened to overrun the airfields ).