The M.9A Master I was based on the M.9 Kestrel trainer that was first demonstrated at the Hendon Air show in July 1937, although it never entered production. The M.9 Kestrel, powered by the 745 hp (555 kW) Rolls-Royce Kestrel XVI V-12 engine, could reach 296 mph (477 km/h). The Air Ministry had selected the de Havilland Don as its advanced trainer, but this proved to be a failure, and the RAF placed a £2 million order for 500 examples of a modified version of the Kestrel, the M.9A Master. Miles rebuilt the prototype M.9 to form a prototype for the Master, fitting a lower powered (715 hp (535 kW)) Rolls-Royce Kestrel XXX engine, of which there were large surplus stocks available, and with extensive revisions to the airframe, which included a new cockpit canopy, a modified rear fuselage and tail, and moving the radiator from under the nose to under the centre-section of the wing. These modifications significantly reduced the aircraft's speed, but it remained one of the fastest and most maneuverable trainers of its day. The first true production Master I made its maiden flight on 31 March 1939. The Master entered service just before the start of the war, and eventually 900 Mk. I and Mk. IA Masters were built. This total included 26 built as the M.24 Master Fighter which were modified to a single-seat configuration, and armed with six .303 in machine guns for use as an emergency fighter, but did not see combat.
When production of the Kestrel engine ceased, a new variant of the Master was designed to use the 870 hp (650 kW) air-cooled radial Bristol Mercury XX engine. The first M.19 Master II prototype flew on 30 October 1939 and 1,748 were eventually built. When the Lend-Lease programme began to supply engines from the United States, a third variant of the Master, the M.27 Master III was designed, powered by the American 825 hp (615 kW) Pratt & Whitney Twin Wasp Junior two-row radial engine. A total of 602 Master IIIs were built before production of the Miles Martinet took over in 1942.
In trainer form, the Master was equipped to carry eight practice bombs, plus one .303 in Vickers machine gun mounted in the front fuselage. In 1942, all variants had their wings clipped by three feet (one metre) to reduce stress on the wings and increase maneuverability.