A few weeks after the start of World War II in September 1939, she helped to sink one German submarine and then participated in the Second Battle of Narvik during the Norwegian Campaign of 1940.

The ship helped to sink another German submarine before she was transferred to the English Channel to protect convoys during the Normandy landings.

Forester carried a maximum of 470 long tons (480 t) of fuel oil that gave her a range of 6,350 nautical miles (11,760 km; 7,310 mi) at 15 knots (28 km/h; 17 mph).

On 27 April, Forester attempted to shepherd the British merchant Consett to Santander, but the cargo ship was shelled by the battleship España and forced out of the territorial waters.

Two days later, Forester was one of the screen for the battleship Rodney and the battlecruiser Renown as they sailed back to Scapa Flow to refuel.

[14] In late June, the 8th DF was ordered to Gibraltar where they were to form the escorts for Force H.[7] A few days later, they participated in the attack on Mers-el-Kébir against the Vichy French ships stationed there.

[16] A month later Forester was one of the escorts for Force H during Operation Hurry, a mission to fly off fighter aircraft for Malta and conduct an airstrike on Cagliari on 2 August.

[17] She then returned to Gibraltar and escorted the aircraft carriers Argus and Ark Royal during Operations Coat and White in November.

[18] On 21 November, the light cruiser Despatch, Forester and Faulknor intercepted the Vichy French blockade runner MV Charles Plumier and escorted her to Gibraltar.

[19] The ship escorted Force F to Malta during Operation Collar later in the month and participated in the inconclusive Battle of Cape Spartivento on 27 November.

This did not last long as they were ordered to escort Convoy SL 67 and the battleship Malaya en route back to Gibraltar.

[22] The following month Forester was part of the escort screen, with five other destroyers, for the battleship Queen Elizabeth and the light cruisers Naiad, Fiji and Gloucester which were joining the Mediterranean Fleet.

This was part of Operation Tiger which included a supply convoy taking tanks to Egypt and the transfer of warships to and from the Mediterranean Fleet.

[23] Later that month, she participated in Operation Splice, another mission in which the carriers Ark Royal and Furious flew off fighters for Malta.

[24] Force H was ordered to join the escort of Convoy WS 8B in the North Atlantic on 24 May, after the Battle of the Denmark Strait on 23 May, but they were directed to search for the German battleship Bismarck and the heavy cruiser Prinz Eugen on 25 May.

In late June, Forester screened Ark Royal and Furious as they flew off more fighters for Malta in Operation Railway.

[25] On 23 July, during a Malta supply convoy (Operation Substance), Forester rescued survivors from her sister Fearless, which had been attacked by Italian torpedo-bombers, and then sank the wrecked and burning ship with torpedoes.

Upon her return to the UK on 26 October, the destroyer was briefly assigned to the 11th Escort Group before rejoining the Home Fleet at Scapa Flow in November.

The ship remained on convoy duty in the North Atlantic until 29 May when she was transferred to the English Channel to support the Normandy landings for the next several months.

She was turned over to the British Iron & Steel Corporation on 22 January 1946 for disposal and arrived at Rosyth to be broken up for scrap on 26 February by Metal Industries, Limited.