It was an all-metal, twin-engine, low-wing monoplane with retractable landing gear, armed with three flexible machine guns, one each in the nose, dorsal turret, and ventral gondola.

The radically revised second prototype which flew on 5 May 1937 eventually formed the basis for series production, with aircraft being manufactured by SNCASO, the nationalised company that had absorbed Bloch and Blériot.

A four-engined derivative of the MB.134, was developed powered by four 530 kW (710 hp) Gnome-Rhône 14M 14-cylinder radial engines, with an essentially similar airframe.

Upon the outbreak of the war, the metropolitan Groupes suffered many losses in attempts at daylight reconnaissance of Germany's western borders.

Twenty-one unserviceable aeroplanes were reported captured by the Luftwaffe but photographic evidence suggests at least a few flew for the Nazis.