John was educated at Stancliffe Hall, Co Derby (1899-1901), at Loretto, Musselburgh (1901-1906) where he gained the Choral Scholarship, and at Sheffield University (1906-1911), where he graduated M.B., Ch.B. He then became House-surgeon at the Sheffield Royal Infirmary from 1911-1913, and afterwards was the Assistant Medical Officer of the Southwark Union Infirmary, East Dulwich. On 3rd June 1912, John joined the Territorial Force at the rank of Lieutenant but then transferred to the R.A.M.C. on 30 January 1914. He disembarked for France on 9th September, and served with a field ambulance, becoming attached to the 1st Bn. Hampshire Regiment soon after. He was mentioned in Sir John French's Despatch, and was awarded the Military Cross due to rescuing a soldier under heavy shell fire, whose leg he saw was shot off by a "Jack Johnson" whilst his comrade was blown to pieces. John instantly rushed out and carried the man to safety. John gained promotion to Captain on 30th March 1915. After his death, the 'Hampshire Regiment Journal' in August 1915 stated: "We have to record another heavy loss to this battn., which has suffered so many. Our 'doctor' Capt Gwynne, was shot through the head by a sniper when on an errand of mercy. On the night of 8-9 July, the battn. was relieved...... in the trenches captured by the brigade from the Germans on the 6th. Capt Gwynne went up to the trenches shortly after daybreak, to ascertain whether all the wounded had been evacuated. Several had not been observed in the dark, and he attended to each of them. He was informed that a bomber of the Rifle Brigade was lying with his hand blown off in a shallow trench, which was not approachable in daylight. Reckless as ever of his personal safety when a wounded man was in question, he proceeded there and had accomplished his task, when a sniper shot him through the head. Capt Gwynne, with one exception, was the senior member of the battn. in point of service out here, he having joined us at Chateau de Fontenelles, near Ligny, during the retreat. We all considered him as one of the battn., and for a long time he had been performing the thankless task of Mess President. A friend of all, with the true sympathy to suffering, as all doctors have, we regarded his death as our last and one of our greatest sacrifices to the Ypres Salient." A brother officer wrote: "Gwynne seems to have made an enormous reputation for his courage. The whole district round here resounds with his name. The men who knew him here will talk of him to their dying day. I've heard of him all along the Front now. Everywhere he has been excellent at his work, and made a tremendous reputation for courage. And it requires courage to do the things he had done.” John was the eldest son of Dr Charles Nelson Gwynne, M.D., M.A. and Grace Maunsell Gwynne (nee Hanna) of "Upway" 5 Sydney Terrace, Guildford. His younger, and only brother, Lt Owen Perrott Gwynne, 92nd Punjabis, was killed on active service at Mesopotamia six months later at the age of 25.