Mellette was launched by Oregon Shipbuilding Corp., Portland, Oregon, 4 August 1944; sponsored by Mrs. Clarissa Bickford; acquired from the Maritime Commission on a loan‑charter basis; and commissioned 27 September 1944, Commander F. H. Spring, USNR, in command. In November 1944, Mellette followed a San Pedroshakedown cruise with a voyage to the Hawaiian Islands for training operations. She conducted amphibious troop, gunnery, and tactical exercises off Maui into January 1945. On 27 January she joined TG 51.1 and got underway for Iwo Jima. With units of the 4th Marine Division embarked, she steamed west, via Eniwetok and Saipan, arriving off the Volcano Islands to participate in the initial assault 19 February. She remained off the eastern beaches of Iwo Jima for the next 6 days, unloading supplies and taking on casualties. On the 25th she sailed for Saipan where she disembarked her wounded passengers and began preparations for the upcoming Okinawa campaign. Through the next month Mellette trained off Tinian's western beaches with TG 51.2 and on 27 March weighed anchor and headed for the Ryukyus. On 1 April she was off Okinawa and at 0631 commenced disembarking units of the 2d Marine Division in diversionary landings along the island's southeastern coast. Her mission completed by mid‑morning, she reembarked her Marines and sailed to the main assault area to stand by until needed. There she remained until ordered back to Saipan on the 11th. She disembarked the Marines at Saipan on the 14th and remained there until 4 June when she began carrying men and cargo among the Marianas and Solomons. In July she carried reinforcements, the Army's24th Infantry Regiment, to Kerama Retto. Back at Saipan when the Japanese capitulation was announced, 15 August, Mellette immediately took on men of the 6th Marine Division and sailed for Honshū. Arriving with the first wave of occupation troops, she disembarked the Marines at Yokosuka Naval Base on the 30th, witnessed official surrender in Tokyo Bay2 September, and then returned to Saipan to take on men of the 2d Marine Division for transportation to Nagasaki. Next assigned to “Magic Carpet” duty, she completed two voyages between the western Pacific and Seattle before 21 January 1946 when she got underway for the east coast and inactivation. Arriving at Norfolk, Virginia, 3 February, she decommissioned 25 June and entered the Reserve Fleet at Yorktown, Virginia.
With the outbreak of hostilities in Korea, Mellette was reactivated, recommissioning 18 October 1950. For the next 4 years she operated primarily along the east coast, participating in fleet operations and exercises from Nova Scotia to the Caribbean. During that period she served with the 6th Fleet in the Mediterranean8 September 1953 to 4 February 1954.
