Baron Kiichirō Hiranuma (平沼 騏一郎, 28 September 1867 – 22 August 1952) was a Japanese lawyer and politician who served as Prime Minister of Japan in 1939.

After the Japanese surrender, he was sentenced to life imprisonment by the International Military Tribunal for the Far East for his role in World War II.

Like the Mito scholars, Hiranuma believed that Japan possessed a particular essence, the kokutai, characterised by the moral bond between the nation and the Emperor as a sacred ruler.

Hiranuma established a reputation during his time at the Ministry of Justice as a strong opponent of government corruption, and successfully handled a number of high-profile cases.

[5] Hiranuma was highly outspoken against corruption and immorality in Japan's political parties, and that attitude soon expanded to include what he saw to be foreign threats, such as socialism and liberal democracy.

[5] Hiranuma was appointed Minister of Justice in the second cabinet of Gonnohyōe Yamamoto, formed in the aftermath of the Great Kantō earthquake in September 1923.

Hiranuma resigned along with rest of the cabinet in January 1924 to take responsibility for the lapse in security represented by the Toranomon incident, in which a communist attempted to assassinate Crown Prince Hirohito.

The incident gave Hiranuma a renewed vigilance towards what he considered subversive ideology and for this reason he formed the Kokuhonsha, a political organisation with the intention of defending the kokutai.

This organisation gathered a broad range of influential figures, including General Sadao Araki, Admiral Kanji Katō, Kisaburo Suzuki, Yoshimichi Hara and Harumichi Tanabe.

Hiranuma and his clique were the driving force behind the adoption of the Peace Preservation Law, intended to combat communism and other threats to the kokutai.

In 1931, he rallied support within the government for the Imperial Japanese Army after it had seized control of Manchuria without prior authorization, and he later helped in the creation of Manchukuo.

[11] When Kuratomi retired in May 1934 he recommended Hiranuma as his successor, but due to Saionji's opposition the Imperial Household Minister Kitokurō Ichiki was appointed instead.

With the signing of the German-Soviet Non-Aggression Pact in August 1939, Hiranuma's cabinet resigned over that foreign policy issue and over the massive defeat of the Japanese Army in Mongolia during the Nomonhan Incident against the Soviet Union.

Hiranuma became a central figure in a conservative reaction against the New Order Movement promoted by Fumimaro Konoe since his reappointment as prime minister in July 1940.

Hiranuma declared: "We should research the ancient rites in detail and consider their application in administrative affairs in general and the common life of the nation.” Hiranuma was strongly opposed to the political and diplomatic actions of Foreign Minister Yōsuke Matsuoka and to the Tripartite Pact concluded between Imperial Japan, Nazi Germany, and Fascist Italy in September 1940.