During World War II, both "Giulio Cesare" and her sister ship, , participated in the Battle of Calabria in July 1940, when the former was lightly damaged. They were both present when British torpedo bombers attacked the fleet at Taranto in November 1940, but "Giulio Cesare" was not damaged. She escorted several convoys to North Africa and participated in the Battle of Cape Spartivento in late 1940 and the First Battle of Sirte in late 1941. She was designated as a training ship in early 1942, and escaped to Malta after the Italian armistice the following year. The ship was transferred to the Soviet Union in 1949 and renamed Novorossiysk (). The Soviets also used her for training until she was sunk in 1955, with the loss of 608 men, when an old German mine exploded. She was salvaged the following year and later scrapped.