Born in Otago in New Zealand, MacKenzie joined the RAF in 1937 on a short service commission. After completing his flight training, he was posted to No. 41 Squadron where he flew Hawker Furys and then Supermarine Spitfires. He flew several patrols covering the beaches at Dunkirk during Operation Dynamo and then fought in the Battle of Britain, during which he destroyed several German aircraft. He was later sent to Singapore to join No. 488 Squadron, raised to strengthen the aerial defences of British Malaya. The squadron flew extensively during the Japanese invasion of British Malaya but was eventually evacuated to Australia. Mackenzie then commanded No. 14 Squadron before returning to the United Kingdom in mid-1943. He transferred to the Royal New Zealand Air Force in 1944, briefly commanded No. 64 Squadron, and finished the war in New Zealand. He later rejoined the RAF, serving in a number of training posts until his retirement from the military in 1957 with the rank of squadron leader. Returning to New Zealand, he ran an automotive dealership in Balclutha in his later years. He died in 1993.