In a brief training period off the Virginia coast, she prepared for the Casablanca invasion, but a turbine casualty prevented her participation in the initial landings.

After five months in the Mediterranean, Nicholson returned to the United States for overhaul in preparation for Pacific deployment, for which she sailed from Boston early in January 1944.

Throughout the long New Guinea campaign, a matter of successive assaults on coastal points and nearby islands, Nicholson gave gunfire support to troops ashore.

She had similar duty in the Admiralties; when, during the conquest of Seeadler Harbor, she was assigned to draw fire from an enemy battery on Hauwei Island.

Returning to the western Pacific in February 1945, Nicholson escorted ships passing between Guam and Ulithi, and arrived off Okinawa for its invasion late in March.

Serving in the exposed radar picket line, Nicholson came through untouched by kamikazes, but rescued survivors from stricken destroyers Little and Morrison.

Rejoining the 3rd Fleet for the final air operations against the Japanese home islands, Nicholson was off Honshū at the war's end.