Educated at Hurstpierpoint College, he entered RAF College, Cranwell in September 1932 as a Flight Cadet and graduated in July 1934 with a permanent commission. He was posted to No 54 Squadron at Hornchurch.
In 1936 MacDonell was posted to No 802 (Fleet Fighter) Squadron, based on shore at Hal Far, Malta and at sea on HMS Glorious. He later went to RAF Gosport as an instructor before serving at the Air Ministry.
On 30 June 1940 MacDonell arrived at 5 OTU, Aston Down. After converting to Spitfires, he was posted to No 64 Squadron at Kenley on 19 July as a supernumerary.
On 25 July MacDonell claimed a Ju 87 destroyed. On this day 64’s CO, Squadron Leader N C Odbert, flew his last sortie before a posting to Northern Ireland, and MacDonell assumed command on the 26th or soon after.
On the 29th he destroyed a Ju 87 and a Bf 109 and damaged another Bf 109, on 5 August he destroyed a Bf 109 and probably another, on the 8th he probably destroyed two Bf 109s, on the 11th destroyed a Bf 109 and damaged another and on the 15th he destroyed a Bf 109 and damaged another.
MacDonell destroyed a Bf 109, probably another, damaged a third, shared a He 111 and damaged another on the 16th. On this day he was shot down by a Bf 109. He baled out, unhurt, landing at Possingworth Park, Heathfield, Sussex. His Spitfire crashed at Blackboys, Uckfield. MacDonell destroyed a Do 17 and damaged a Ju 88 on the 18th and was awarded the DFC on 6 September.
On 11 November MacDonell damaged a Bf 109 and on the 29th destroyed another, his final victory. He was portrayed by Cuthbert Orde.
In March 1941, on a sweep over France, MacDonell was shot down by the German ace Werner Mölders. He baled out and was taken prisoner. Freed in April 1945, he received a Mention in Despatches for distinguished services while a PoW.
MacDonell was made CB in 1964 and retired from the RAF on 15 November 1964 as an Air Commodore. He was a long serving Chairman of the Battle of Britain Fighter Association and died on 7 June 1999.
