Middlesex was commissioned at Port Arthur on June 8, 1944, arrived at Halifax in mid-July and sailed for Bermuda in August to work up. Assigned to EG W-3 of Western Escort Force, she joined the group in New York on August 30, direct from Bermuda. Middlesex was principally engaged as southern local escort to U.K.-bound convoys out of New York. She was Senior Officer's ship from mid-November 1944, until the force was disbanded in June, 1945. Afterward, she refitted at Halifax and was placed in maintenance reserve there. In March, 1946, she returned to service as emergency ship at Halifax. On December 2, 1946, en route to assist the fishing vessel Ohio, she ran ashore on Half Island Point, near Halifax, and was declared a total loss.