In the 1930s, the French Air Force realized that in order to remain competitive with the air forces of neighboring countries, they would need to develop a new fighter aircraft. Their current aircraft, the Dewoitine D.510, was considered obsolete despite not having seen service, due to the significant advances in aviation technology. Because of this perceived inadequacy, in 1934, a contract was put forth to develop a new fighter.

The Dewoitine company (Constructions Aéronautiques Émile Dewoitine) initially responded by submitting an improvement on the D.510, which was designated as the D.513. However, it was deemed inferior to the M.S. 405, a competing aircraft built by Morane-Saulnier. Two years later, the French Air Ministry put forth another specification for a new fighter, and Dewoitine responded with another design. However, it was rejected by the Air Ministry because the specifications had been changed yet again.

Finally, in 1937, the Air Ministry launched another technical programme, designated A.23. Designs were submitted by Morane-Saulnier, Loire-Nieuport, Caudron-Renault, Bloch, Arsenal, and Dewoitine. Dewoitine's design would go on to become the D.520 but there was still a long road ahead. That same year, Dewoitine had become a part of the manufacturing consortium Société nationale des constructions aéronautiques du Midi (SNCAM), and the manufacturing programmes put forth by the French Air Force kept on changing.

In 1938, the first D.520 prototype finally flew but suffered from significant problems with speed and engine temperatures. After many redesigns, a contract for production of 200 D.520s was issued in March 1939, and another contract for an additional 510 aircraft was finalized in July of that year. Additionally, Belgium and Poland were interested in the new French fighter. Unfortunately, most of the initial batch of D.520s failed acceptance tests, necessitating another redesign. During 1940, plans had been devised for a lighter version of the aircraft, designated the D.521. Negotiations were also opened up with the American company Ford to produce a licensed version that would have been designated as the D.522.

Although a potent fighter and more than a match for the German Messerschmitt Bf 109, the D.520s were not available in sufficient numbers to greatly affect the outcome of the battle of France in 1940; when the German forces first invaded on 10 May 1940, only 36 D.520s had been dispatched out of 79 available (by this point, a total of 246 had been manufactured, but many were sent back after being deemed unsatisfactory). During the battle of France, the D.520 performed admirably, with 114 air victories and 39 probables claimed for 85 aircraft lost. When the armistice was signed in June 1940, production of the D.520 continued, but the D.521 and D.522 projects were cancelled. In total, a little over 900 D.520s were produced.

After France fell, D.520s were used both by the Vichy France puppet government (controlled by the Nazis) and later by the Free French Forces. Vichy French Air Force pilots flew the D.520 in the North Africa against British, Free French, and American pilots. However, their combat capabilities were greatly diminished due to a lack of supplies. (Aircraft from the USS Ranger, mentioned in my post on the SB2U Vindicator, fought against Vichy D.520s near Casablanca). After formerly Vichy forces in North Africa and mainland Europe sided with the Allies, D.520s fought against the Luftwaffe.

In addition to being used by French (both Vichy and Free) forces, the D.520 was used by the German Luftwaffe, Italy's Regia Aeronautica, and the Bulgarian air force. After WW2, D.520s remained in service in the French Air Force as training aircraft, finally being retired from service in 1953.