Newmarket departed Halifax on 15 January for the United Kingdom, calling at St. John's and arriving at Belfast on the 26th and at Plymouth, England, on the 30th.

After a short refit on the Humber, she began convoy escort work in the Western Approaches Command and on 2 June 1941, was unsuccessfully attacked by an aircraft in the northwestern approaches. Later that month she proceeded to Sheerness, and was in dockyard hands until November when she joined the 8th Escort Group, at Londonderry.

On 3 January 1942, Newmarket had to leave Convoy H.X. 166 because of boiler trouble, and proceeded to Lough Foyle. On the 30th she arrived at Liverpool, and was under refit until the end of March.

In April 1942, she escorted the Russian convoy P.Q. 14, but, a month later, was allocated for duty as an aircraft target ship in the Firth of Forth. She refitted at Leith between December 1942 and February 1943, and later in the year, refitted again at Rosyth, Scotland. In September 1943, Newmarket was reduced to care and maintenance status at Rosyth but resumed duty as an aircraft target ship from the spring of 1944, until after the end of the war in Europe. She was scrapped at Llanelly in September 1945.