On his return to Japan, he was assigned to the Imperial Japanese Army General Staff, in charge of British and American military intelligence.

With the start of the Second Sino-Japanese War, he was a field commander during the China Incident of July 1937.

[1] On 15 July 1938 he was promoted to major general, and assigned command of the IJA 6th Infantry Brigade.

During the resulting Guadalcanal campaign, Maruyama led troops during the October 1942 Matanikau action and the subsequent Battle for Henderson Field, in which Maruyama's troops were decisively defeated.

Maruyama remained in command of 2nd Division until the beginning of June 1943, when he was transferred to the Imperial Japanese Army General Staff under Field Marshal Hajime Sugiyama.