Mamoru Shigemitsu was a Japanese diplomat and politician in the Empire of Japan, who served as the Japanese Minister of Foreign Affairs at the end of World War II and later, as the Deputy Prime Minister of Japan.
Shigemitsu was highly critical of the foreign policies of Yōsuke Matsuoka, especially the Tripartite Pact, which he warned would further strengthen anti-Japanese sentiment in the United States. Shigemitsu spent two weeks in Washington DC, on the way back conferring with Ambassador Kichisaburō Nomura to try unsuccessfully to arrange for direct face-to-face negotiations between Prime Minister Fumimaro Konoe and US President Franklin D. Roosevelt.
Shigemitsu's many attempts to stave off World War II angered the militarists in Tokyo and only two days after the attack on Pearl Harbour, Shigemitsu was sidelined with an appointment as ambassador to the Japanese-sponsored Reorganized National Government of China. In China, Shigemitsu argued that the success of the proposed Greater East Asia Co-Prosperity Sphere depended on the equal treatment of China and other Asian nations with Japan.
On April 20 1943, in a move that was viewed as a sign that Japan might be preparing for a collapse of the Axis Powers, Japanese Prime Minister Hideki Tōjō replaced Foreign Minister Masayuki Tani with Shigemitsu, who had been steadfast in his opposition to the militarists. He was thus foreign minister during the Greater East Asia Conference. The American press often referred to him in headlines as "Shiggy".
From July 22, 1944, to April 7, 1945, he served simultaneously as Minister of Foreign Affairs and Minister of Greater East Asia in the Koiso administration. He again held that post briefly in August 1945 in the Higashikuni administration.
Shigemitsu as civilian plenipotentiary, along with General Yoshijirō Umezu, signed the Japanese Instrument of Surrender on September 2nd 1945.