He served his midshipman duty aboard the cruisers Hashidate and Nisshin, and after being commissioned as an ensign on 20 December 1906, he was assigned to the destroyer Asatsuyu.

He subsequently served in a number of staff positions, was promoted to captain on 1 December 1925, and received his first command: the cruiser Yura in 1926.

From December 1931 to February 1933, Toyoda was chief of the Second Section of the Imperial Japanese Navy General Staff, and promoted to vice admiral on 15 November 1935.

Promoted to full admiral on 18 September 1941, at the time of the attack on Pearl Harbor, Toyoda was Commander-in-Chief of the Kure Naval District.

[3] On 10 November 1942, Toyoda became a member of the Supreme War Council, where he made a strong (but mostly unsuccessful) effort to increase funding and the capacity of Japan's industry toward naval aviation, over the opposition to the Army-dominated Imperial General Headquarters.

In June of the same year, he drafted and implemented "Plan A-Go" which resulted in the decisive defeat of the Imperial Japanese Navy under the command of Admiral Jisaburō Ozawa in the Battle of the Philippine Sea.

Nonetheless, Toyoda continued with the same strategy, approving "Plan Ten-Go" to send the battleship Yamato on its one-way final mission to Okinawa.

Initially, the Navy Minister, Mitsumasa Yonai, hoped that Toyoda would be able to exert a moderating influence over Army Chief of Staff Yoshijirō Umezu (since both came from the same district of Japan).

He was viewed as "highly intelligent and widely informed", and was observed to be a strong critic of the amount of political power the Army held in the Japanese government.