Under orders from Prince Kan'in Kotohito, Wakamatsu was sent to Berlin, where he was involved in the forging of the Anti-Comintern Pact.

[1] As a general, Wakamatsu served in various army and army group level staff officer positions until he was appointed as the Vice Minister of War in April 1945, during the last months of the Pacific War.

In August 1945 he was involved in the Kyūjō incident and played a role in ensuring that the army followed Hirohito's orders to surrender.

[3] In July 1948, he was arrested on suspicion of being involved in the mistreatment of Allied prisoners of war (POWs) on hell ships.

After being tried as a Class B war criminal, he was found guilty and sentenced to prison.