F/O Hart was born in Sackville, New Brunswick, Canada.
After learning to fly at Halifax Flying Club, John joined the RAF on a short service commission in January 1939.
John joined 54 Squadron at Catterick in mid-September 1940, but soon afterwards joined 602 Squadron at Westhampnett.
On 29th October, he claimed a Bf 109 destroyed and on 13th November shared a Ju 88.
In early 1941, John was with temporarily with 91 Squadron at Hawkinge, and then returned to 602 Squadron. Following this he went to an OTU as an instructor.
John was given command of 67 Squadron from May to July 1943.
From April to August 1945 he was given command of 112 Squadron in Italy.
On 22nd June 1945, John was awarded the DFC.
John Hart was released from the RAF in 1946 with the rank of Squadron Leader.