Mackenzie was 29 years old, and a sergeant in the 2nd Battalion, The Seaforth Highlanders (Ross-shire Buffs, Duke of Albany's), British Army, employed with the West African Field Force during the Third Ashanti Expedition when the following deed took place for which he was awarded the VC.

On 6 June 1900 at Dompoassi, Ashanti (now Ghana), Sergeant Mackenzie, after working two Maxim guns under heavy fire and being wounded while doing so, volunteered to clear the stockade of the enemy.

[1] John Mackenzie enlisted in the Seaforth Highlanders in August 1887, and served with the regiment in India, including the 1895 Chitral Expedition.

Promoted corporal in May 1897, he was seconded for service in West Africa in November that year, where he was awarded the Distinguished Conduct Medal.

He was promoted to major in April 1914[2][4] and was commanding officer of the 2nd Battalion of the Bedfordshire Regiment, where at Festubert on 17 May 1915, when leading his men, he was killed just after he had left the jumping off trench.