"Glowworm" was in Alexandria when World War II began in September 1939. In October the flotilla was transferred to the Western Approaches Command and "Glowworm" sailed for the UK on 19 October with her sisters , , and . They arrived at Plymouth on 22 October and were deployed in the South Western Approaches. "Glowworm" carried out convoy escort duties and anti-submarine patrols until 12 November when she was transferred to the 22nd Destroyer Flotilla, based at Harwich, for North Sea patrol and escort duties. On 22 February 1940 she was hit by the Swedish ship "Rex" in fog whilst at anchor off Outer Dowsing. "Glowworm" suffered significant structural damage and was under repair at a commercial dockyard in Hull until late March. On completion of the repairs, she was transferred back to the 1st Destroyer Flotilla of the Home Fleet, rejoining the flotilla at its base at Scapa Flow on 20 March.