The IMAM Ro.51 was developed by Industrie Meccaniche Aeronautiche Meridionali (IMAM), a company that originated as Officine Ferroviarie Meridionali (OFM) and later operated as Industrie Aeronautiche Romeo before becoming IMAM in 1934. Under the direction of chief designer Engineer Giovanni Galasso, the Ro.51 was created to compete in the 1936 Regia Aeronautica "R" contest, which sought a new monoplane fighter capable of reaching speeds of at least 450 km/h. This competition featured several other notable Italian designs, including the Fiat G.50 and Macchi C.200.
Two prototypes were ordered in 1937, identified by military serials MM.338 and MM.339. The aircraft utilized a mixed construction, pairing a metal fuselage with wooden wings. The first prototype was equipped with a fixed, spatted main undercarriage, which limited its maximum speed to approximately 467 km/h at an altitude of 5,000 meters. To improve performance, the design was modified to include retractable landing gear; the second prototype, MM.339, was built with this feature from the outset. This modification increased the aircraft's maximum speed to roughly 489 km/h at 5,000 meters.
Power was provided by a Fiat A.74 R.C.38 14-cylinder, two-row, air-cooled radial piston engine, producing approximately 829–840 hp, driving a three-bladed, variable-pitch metal propeller. For armament, the Ro.51 carried two 12.7 mm Breda-SAFAT machine guns mounted in the fuselage and synchronized to fire through the propeller disk.
Despite the improvements offered by the retractable gear, the Ro.51's performance and handling—particularly its climb and maneuverability—were judged inferior to its competitors. It was considered obsolete by the time it first flew in late 1937, leading to its abandonment in favor of more advanced types. While a floatplane variant was studied and trialed, the Ro.51 never entered operational service or saw combat. No airframes are known to have survived.