Details from the regiment were called out on service on 26 August 1939 and on active service on 1 September 1939 as
The Governor General's Horse Guards, CASF (Details), for local protection duties. Those details called out on active service disbanded on 31 December 1940. Subsequently, the regiment mobilized as the 2nd Canadian Motorcycle Regiment, CASF (GGHG) for active service on 24 May 1940. It converted to armour and was redesignated as The Governor General's Horse Guards, CASF on 9 February 1941; as the 3rd Armoured Regiment (The Governor General's Horse Guards), CASF on 11 February 1941; as the 3rd Armoured Reconnaissance Regiment (The Governor General's Horse Guards), CAC, CASF on 1 January 1943; and as the 3rd Armoured Reconnaissance Regiment (The Governor General's Horse Guards), RCAC, CASF on 2 August 1945. It embarked for Britain on 9 October 1941 and landed in Italy on 19 December 1943 as part of the 5th Armoured Brigade,
5th Canadian Armoured Division. On 20 February 1945 the regiment moved with the I Canadian Corps to North-West Europe as part of OPERATION GOLDFLAKE, where it continued to fight until the end of the war. The overseas regiment disbanded on 31 January 1946. The Regiment lost 71 Killed and 210 wounded in the war.