John was educated at Newtonmore and Kingussie Higher Grade School; at George Watson's College, Edinburgh; and at Edinburgh University, where he became a student in Arts and Medicine from 1903 – 1912 – qualifying M.A. in 1907 and M.B., Ch.B., with distinction in December 1912. He won the Crichton Scholarship for four years, and the London Inverness-shire Association Bursary, afterwards holding appointments at the Edinburgh Royal Infirmary, Bangour Institution, and the Dispensary, Carlisle. He was also a keen sportsman and well-known athlete, generally considered as one of the finest shinty players in Scotland, and gaining the Australasian Cup at International Hockey and athletics - Long Jump. He was one of the Edinburgh University representatives in the Scottish Inter-University Matches in 1909, 1910 and 1911. When war broke out John was studying for his D.P.H. but volunteered his services and on 10th October 1914, his name appeared in the London Gazette under the rank of temporary Lieutenant. He entered the war in the Dardanelles as Medical Officer to the 9th Bn. Royal Warwickshire Regiment. John was seriously wounded and being evacuated via a hospital ship when he died. His commanding officer wrote to his family: “The regiment was resting in reserve (after a spell in the forward trenches). The Turks attached, and at the same time bombarded with their guns all the gullies where they knew our troops were. Several of our men were hit, and were carried in stretchers to a dressing station, where your son was, just in rear of the battalion. He most pluckily continued to dress their wounds under fire until he was badly wounded (and I think several of his stretcher-bearers).” Major D S Skelton also wrote: “I was Deputy Assistant Director of Medical Services of the 13th Division in Gallipoli when Lieut J Cattanach, R.A.M.C., was wounded, and, as such, not only out there, but during the training at Blackdown, I had a great deal to do with him. I cannot tell you how sorry and grieved I was to read of his death….. I feel it almost impertinent of me to say how much his regiment liked him, and what a guide and friend he was to all – officers and men. As the superior officer with whom he had mostly to deal, I can only add that I held him to be an exceptionally able young officer, one of the very best regimental Medical Officers with the Division, and I can say this for the Assistant Director, that he thought the same as I.” John was buried at sea. He was the third and youngest son of William Cattanach and Annie (daughter of Donald Kennedy) of Newtonmore, Merchant.