Kuninori Marumo was born on 2 October 1891 in Nagano Prefecture. He graduated from the Imperial Japanese Naval Academy in July 1912 with the 40th class. As a midshipman he served in the cruiser Soya and the battleship Kashima. After he was commissioned an ensign he joined the battleship Mikasa, completed the basic courses at the naval gunnery and torpedo schools, and then went to the battleship Aki.
In 1917, during the First World War, he sailed with the Second Special Task Force, the Japanese destroyers based at Malta under Kozo Sato to assist the Allies in the Mediterranean. In the years that followed he specialized in gunnery, serving as secondary-battery officer in Yakumo and Yamashiro and as gunnery officer in the cruiser Kako, with staff duty in the Second Fleet and the Navy Ministry between sea tours. Promoted to captain in November 1933, he spent the next eight months on an official tour of the United States and Europe. He returned in the summer of 1934 as an instructor at the Yokosuka Air Group, and in November 1935 he became chief of the second section in the Navy Ministry's Bureau of Education.
His only command of a ship began on 15 December 1937, when he took the heavy cruiser Ashigara. He left her in 1938. That October he became chief of the personnel bureau at Kure and personnel chief of the Kure Naval District. He was promoted to rear admiral on 15 November 1939. After further staff duty ashore, he joined the staff of the Fourth Fleet at Truk on 20 November 1941.
On 1 December 1941 Marumo took command of Cruiser Division 18. The division was the light cruisers Tenryu and Tatsuta. He was not captain of either ship. The Pacific War began a week later, and the division moved with the Fourth Fleet's first operations in the central Pacific.
Both cruisers were in the Wake attack on 11 December 1941, in support of the force that tried to land troops on the island. Coastal guns and Marine aircraft drove that attempt off. Wildcat fighters damaged three torpedoes on Tenryu's deck and shot up the radio shack in Tatsuta. Neither cruiser was sunk. A second, heavier assault took the island later in the month.
In May 1942 the division went south for the operation against Port Moresby. Marumo's cruisers escorted the force that seized Tulagi at the opening of the Battle of the Coral Sea, then served as the close support group for the transports bound for New Guinea. After the carrier battle the landing at Port Moresby was cancelled, and his ships withdrew with the invasion force.
He left the division on 20 July 1942 for the Maizuru Naval District. On 1 September he became commander of the Yokosuka Guard Unit and of the First Yokosuka Naval Barracks. From 21 December 1942 he was naval attaché in Manchukuo, with a parallel duty inspecting ship construction and weapons for the navy's technical department. Promoted to vice admiral on 1 November 1943, he remained in Manchuria through the rest of the war. He was repatriated on 10 July 1947 and died on 24 June 1985.