Sgt Glendinning was born in County Durham on 5th July 1912 and was brought up by his mother and grandfather in the village of Willington.
John joined the RAFVR on 25th January 1937. He carried out his early training at No 12 Elementary & Reserve Flying Training School (EFTS) at Prestwick on the Ayrshire coast.
He was called up on the 1st September 1939 and sent to 32 E & RFTS at West Hartlepool.

After a month flying the school’s various training aircraft such as Tiger Moths, Hawker Harts, Hawker Hinds and Miles Magisters, John moved on to 5 FTS at Sealand on 7th October for an assessment of his flying capabilities after which he moved further into Wales when he was posted on 17th December 1939 to 9 BGS (Bombing & Gunnery School) at Penrhos on the west Welsh coast as a staff pilot.
John Glendinning was one of the men who volunteered for training and on 3rd September 1940 he arrived at 7 OUT Hawarden, another Welsh station, known as the Spitfire School.

After Hawarden John’s first Fighter Command posting in mid September 1940 was to the small airfield of Catterick to join his new unit. A few days previously Al Deere’s 54 Squadron found themselves and their Spitfires there after being taken out of the front line. John’s stay at Catterick was very short lived and he was soon posted on to another Spitfire squadron who had fought from Hornchurch for the first year of the war. He travelled two hundred miles south to Biggin Hill where on 23rd October he joined 74 Squadron.

The famous Tigers, renowned throughout the RAF and by the pubic as a very successful and aggressive unit, were led by the South African Sailor Malan, a man noted for tight discipline both in the air and on the ground. The Squadron had moved back south from Norfolk only five days before and was very much in the front line at the hilltop airfield, flying daily standing patrols. John Glendinning‘s first recorded operational flight on Sunday 27th October, only four days after his arrival, found him in combat with his new Squadron.
The Germans made an early start and by 0900 had attacked convoys and the London docks and suburbs. The Tigers were scrambled with 66 Squadron and sent to intercept a large force of Me 109s. The Spitfires were led by Malan. Also flying were Nelson, Soars, Churches, Chesters, Scott, Stephen, Boulding, Franklin, Mungo Park, Skinner - and Glendinning whose aircraft, P7366, may have suffered damage as after the combat he had to land away at Gravesend and return to Biggin Hill the next day.

On 14th November, John destroyed two Ju. 87s and damaged an Me 109 whilst performing a highly dangerous and frightening head on attack:
"I was Yellow 3 of 74 Squadron when we were told to intercept approximately 50 to 80 Ju 87s escorted by Me 109s. I followed my Section into the fight and then picked out the leader of three Ju 87s and closed in on a head-on attack. I opened fire at 250 yards range and saw him drop from his section with clouds of smoke covering the whole of the aircraft. Pieces of the aircraft flew in all directions when I was closing in and he dived straight into the sea. I then broke away and attacked another in a bunch of about nine aircraft; again this was a head-on attack and I opened fire and held until I had to break away. His engine was a mass of flames and he was diving steeply when I last saw him. Not one shot was fired at me during both attacks. As I broke away I climbed up a further three thousand feet and was turning to re-attack when I saw an enemy aircraft coming at me from astern. I turned very steeply from side to side and as I was turning to the port an Me 109 flashed past. It was a perfect deflection shot and I saw pieces of his aircraft flying off. When I broke away I turned to try and find him but could not see anything more. AA guns were firing at me the whole time."

John's successes were followed by a Me 109 on the next afternoon, 15th November, after he had already flown two patrols totalling three hours in the air.

While on patrol over Dungeness on Wednesday 12th March 1941, John was shot down and killed. His assailant is believed to have been the famous Luftwaffe ace Major Werner Molders of JG 51. His Spitfire, P7506, crashed at Ivychurch, Kent.