Following the assassination of Prime Minister Inukai Tsuyoshi on 15 May 1932 by fanatical navy officers who thought Inukai far too conciliatory (the May 15 Incident), Prince Saionji Kinmochi, one of the Emperor's closest and strongest advisors, attempted to stop the slide towards a military take-over of the government. In a compromise move, Saitō was chosen to be Inukai's successor. Sadao Araki remained as War Minister and immediately began making demands on the new government. During Saitō's tenure, Japan recognized the independence of Manchukuo, and withdrew from the League of Nations.
Saitō's administration was one of the longer-serving ones of the inter-war period, and it continued until 8 July 1934, when the cabinet resigned en masse because of the Teijin Incident bribery scandal. Keisuke Okada succeeded as prime minister.
Saitō continued to be an important figure in politics as Lord Keeper of the Privy Seal from 26 December 1935, but was assassinated during the February 26 Incident of 1936 at his home in Yotsuya, Tokyo. Takahashi, his predecessor, was shot dead the same day, along with several other top-rank politicians targeted by the rebels.
Saitō was posthumously awarded the Supreme Order of the Chrysanthemum.
Imperial Russia: Order of the White Eagle (May 1, 1908)
Korean Empire: Grand Order of the Plum Blossoms (March 3, 1908)
Korean Empire: Imperial Tour Commemorative Medal (April 1, 1910)
Great Britain: Queen Victoria Diamond Jubilee Medal (December 6, 1897)
Great Britain: Honorary Knight Grand Cross of the Order of the Bath (May 15, 1906)
Kingdom of Prussia: Order of the Red Eagle, Knight 1st Class (February 26, 1907)
Kingdom of Italy: Knight Grand Class of the Order of Saints Maurice and Lazarus (July 1, 1907)
France: Grand Officer of the Legion d'Honneur (December 17, 1907)
Netherlands: Knight Grand Cross of the Order of Orange-Nassau (May 31, 1911)
Holy See: Knight Grand Cross of the Order of St. Sylvester (January 17, 1922)
Republic of Chile: Order of Merit of Chile 1st class (March 22, 1913)
Holy See: Knight Grand Cross of the Order of Pius IX (January 23, 1932)
Manchukuo Empire: National Foundation Merit Medal (March 1, 1934)