In the Second World War Festing was air liaison officer for the expedition to Norway of 1940, then, having been promoted to acting lieutenant colonel in April 1940, as a staff officer in the Operations Directorate at the War Office from May 1940. In September 1940 he became Commanding Officer of the 2nd Battalion East Lancashire Regiment and then in April 1942 he became Commander of 29th Independent Infantry Brigade Group which was the landing force of Force 121 for Operation Ironclad, the seizure of Vichy French ports and airfields in the Indian Ocean, notably Diego Suárez, Majunga and Tamatave in Madagascar. He was awarded the Distinguished Service Order (DSO) for his services in this campaign.