He was a graduate of the 39th class of the Imperial Japanese Naval Academy, ranking 17th of 148 cadets in 1911.

In 1933, Takagi was assigned command of the cruiser Nagara, followed by Takao in 1936 and the battleship Mutsu in 1937.

Takagi was promoted to rear admiral on 15 November 1938, and was Chief of the 2nd Section of the Imperial Japanese Navy General Staff in 1939.

At the start of the Pacific War, Takagi was commanding the naval forces supporting the invasion of the Philippine Islands in late 1941, Takagi headed the task force covering the Java landings in Dutch East Indies.

On 21 June 1943, he was again given a front line assignment, when he was made commander of the IJN 6th Fleet (submarines), based in the Mariana Islands.