Lowestoft served as a convoy escort during the war, both in the North Atlantic and off the west coast of Africa.

On 1 May 1933, the British Admiralty ordered two Grimsby-class sloops, Lowestoft and Wellington to be built at Devonport Naval Dockyard as part of the 1932 construction programme.

[6] The ship could be fitted for minesweeping or minelaying (for which the aft 4.7 inch gun was removed, allowing 40 mines to be loaded) as well as escort duties.

A quadruple Vickers .50 in (12.7 mm) machine gun mount provided close-in anti-aircraft armament.

[10][11] In January 1938, Lowestoft landed sailors at Chefoo (now known as Yantai) to protect Western interests during a Chinese offensive in the region with the aim of retaking Hangzhou during the Second Sino-Japanese War.

[16][17] In July 1939, Lowestoft was refitted at Hong Kong, and was re-armed with 4-inch guns to increase its anti-aircraft capability.

[10] On 2 September 1940, Lowestoft, along with the sloop Scarborough, the destroyers Skeena and Westcott and the corvette Periwinkle, joined inbound Atlantic convoy SC.2 as escort.

U-boats sank four merchant ships before the escort group, consisting of Lowestoft, the corvettes Calendula, Heartsease and La Malouine and the destroyer Shikari arrived.

[20] On 18 November, Lowestoft was escorting Convoy FN336 off the East coast of England, near her namesake town, when she shot down an attacking German aircraft.

She was under repair at Chatham Dockyard until October that year, with the opportunity taken to fit radar and two Oerlikon 20 mm cannon.

In August, Lowestoft transferred to the Western African Command, based at Freetown, escorting convoys along the coast of West Africa.

In order to prepare to use these bases, in early October 1943 the British carried out Operation Alacrity, with a convoy being run to Terceira and Faial islands, carrying stores and personnel to allow the use of these bases for Very Long Range (VLR) maritime patrol aircraft in order to help close the Mid-Atlantic gap, with Lowestoft forming part of the powerful escort for this convoy (including an Escort carrier, nine destroyers and three corvettes).

[24] In June 1944, Lowestoft returned to the United Kingdom for a refit at Dunstaffnage, near Oban in Western Scotland.