Unlike in earlier projects, the Imperial Japanese Army issued in February 1936 detailed specifications that had to be met by the new aircraft. These included a maximum speed 399km/h at 3,000 m (9,840 ft); climb to altitude in under eight minutes; take-off in less than 300 m (980 ft); normal operating altitude from 2,000 m (6,560 ft) to 4,000 m (13,120 ft); and endurance of more than five hours at 299km/h at 3,000 m (9,840 ft). Structural strength was specified as well, including a load factor of 6 while at high angle of attack, and 4 while in a glide. Minimum bombload for short-range missions was to be 1500-1NaN-1 with a variety of load configurations. Loaded, the bomber was to have a weight of less than 1000-1NaN-1. Other specified requirements were a crew of from four to six; engines to be either the Nakajima Ha-5 or Mitsubishi Ha-6; and three gun positions (nose, dorsal and ventral, each with one flexible 7.7 mm (0.303 in) Type 89 machine gun). The Hi-2 (Type 94) or Hi-5 radio, and other details were also specified.
Nakajima's veteran design team included Kenichi Matsumura as chief designer, assisted by Setsuro Nishimura and Toshio Matsuda, all of whom had previous twin-engine design experience on the Nakajima's licensed-produced version of the Douglas DC-2 commercial airliner project, and the short-lived LB-2 long-range attack bomber project for the Imperial Japanese Navy.
The Ki-19 was a mid-wing cantilever monoplane of all-metal construction with fabric-covered control surfaces. The aircraft had a bomb bay within a very streamlined fuselage as opposed to carrying the bombs externally. Douglas-type hydraulically-operated retractable landing gear and split-flaps were used.
Performance testing by the Tachikawa Army Air Technical Research Institute with the competing Mitsubishi Ki-21 lasted from March to May 1937. Evaluation was continued at the Army's main bomber base at Hamamatsu for bombing and other operational testing beginning in June. Not completely satisfied with the combinations of airframe and engines, the Army ordered to both Ki-19 prototypes to be powered by Mitsubishi Ha-6 engines, while the two prototypes of the Mitsubishi Ki-21 also converted to be powered by Nakajima Ha-5 engines.
Prototypes from the two companies were almost identical in performance, but the Army officially selected the Mitsubishi Ki-21 as the "Army Type 97 Heavy Bomber", Nakajima having lost the Army contract.
The fourth prototype was converted to the mail plane in April 1939 it got the new designation N-19. It was commonly referred to as the N-19 Long-Range Communications Aircraft and sold to the Domei Tsushin (Domei Press Agency), under registration J-BACN and was named Domei No.2.