The Bloch MB-150 was first developed in response to a French Air Ministry fighter specification issued in July 1934. It was designed by Maurice Roussel, working for Avions Marcel Bloch. Roussel produced an all-metal low wing monoplane, powered by an 850 hp Gnome & Rhône 14 Kfs air-cooled radial engine. The first prototype was completed in early 1936, but it was not a great success. On 17 July 1936 it failed to leave the ground on what should have been its maiden flight. Meanwhile work had been progressing better on the Morane-Saulnier M.S. 405, and that fighter was adopted by the French Air Force.
1936 also saw the nationalization of part of the French aircraft industry. Avions Marcel Bloch was absorbed into SNCASO. The new organisation resumed work on the MB-150 design in 1937. It finally made its first flight on 4 May 1937, and as a result of the first flight several changes were made, including the replacement of the original landing gear and a slight increase in the size of the wings. The modified aircraft flew on 29 September 1937, but more changes were still needed. This time the main change was an engine change, to a Gnome & Rhône 14N-07, giving 920 hp at 12,140 ft. With this engine the prototype reached a speed of 269 mph in December 1937.
Although the MB-150’s performance was still not impressive, the French Air Force desperately needed modern fighters. The M.S. 405/ 406 was taking longer than expected to enter full production. In April 1938 an order was placed for three prototype aircraft, quickly followed by an order for 25 pre-production machines. Work began on the pre-production machines in May, and it soon became clear that the design of the MB-150 was not well suited to mass production. This resulted in a rapid re-design of the fuselage, to improve the speed of construction. The new aircraft was redesignated as the MB-151.