Soemu Toyoda was born in Japan in 1885. He graduated from the Japanese Naval Academy in 1905, at which time he was appointed a naval cadet. In the years following the completion of his time at the Naval Academy, Toyoda received several naval recognitions and rose in the ranks. By 1941 Toyota had reached the rank of admiral and on September 18, 1941 he was appointed Commandant of Kure Naval District, just three months before the Japanese attack on Pearl Harbor. In November 1942, he became a member of the Supreme War Council and in May 1943 he took command of the Yokosuka Naval District. In May of the following year, Toyoda was appointed Commander-in-Chief of the Combined Fleet, a position he held for just over a year. In early May 1945 he was also appointed commander in chief of the Combined Naval Forces, a position Toyoda held concurrently with his position as commander in chief of the Combined Fleet through May 1945. By the end of the month, Toyoda had been released from his other duties and was appointed chief of the Naval General Staff, a position he held through the end of the war.

In his position as the chief of the Naval General Staff, Toyoda participated in the Imperial Conferences concerning the Japanese surrender. Initially the minister of the navy, Mitsumasa Yonai, wanted Toyoda appointed the Navy chief of staff because of the influence he might have over Yoshijiro Umezu, the Army chief of staff, in the decision to end the war. (Both Umezu and Toyoda had come from the same district of Japan.) Toyoda's opinion concerning the end of the war, however, was different than Yonai anticipated. Toyoda joined Umezu in his protestations against the Potsdam Proclamation of July 26, 1945, which demanded the demobilization of the Japanese armed forces, the allied occupation of Japan, and the trial of Japanese war criminals.

Toyoda was not against the termination of the war but insisted that the Japanese push for more favorable terms. After the dropping of the atomic bombs on Hiroshima and Nagasaki, Toyoda's feelings remained unchanged. With the aid of Emperor Hirohito, an agreement was reached that the Japanese would surrender with the stipulation that the occupying forces not impede the imperial system of government and the powers of the Emperor. A letter to this effect was sent on August 10, 1945. The next day James F. Byrnes, U.S. Secretary of State, returned a letter rejecting the demands made by the Japanese government.

On August 13, Toyoda signed a petition for an Imperial Conference concerning the Japanese surrender on the terms that the conference would not be held for a few days and that he be notified before the petition was actually used. Instead, the next morning the Imperial Conference had been called. During the conference both Toyoda and Umezu are said to have voiced their concerns, particularly regarding the subordinate position the Emperor would play under the terms of surrender. Despite these concerns, Hirohito gave the order to bring the war to an end with an unconditional surrender.

After the war, high level leaders of both the German and Japanese governments were tried for war crimes. Because of Admiral Toyoda's position at the end of the war, he was charged as a war criminal and tried in Tokyo, Japan before a military tribunal in October 1948. Toyoda was charged with violating "the laws and customs of war" (p. 9 of MSS 195 Bx 1 Vol. 1.) The charge specified that Toyoda had:

"willfully and unlawfully disregard[ed] and fail[ed] to discharge his duty as a said officer by ordering, directing, inciting, causing, permitting, ratifying and failing to prevent Japanese Naval personnel of units and organizations under his command, control and supervision to abuse, mistreat, torture, rape, kill, and commit atrocities and offenses against innumerable persons of the United States, its Allies, Dependencies, and other non-combatant civilians" (pp. 9-10 of MSS 195 Bx 1 Vol. 1).

To this charge Admiral Toyoda plead not guilty and was subsequently the only one of the accused Japanese War criminals found not guilty on all counts. In 1957 Toyoda died of a heart attack.