A prominent sportsman from an early age, Myles graduated in medicine at Trinity College Dublin in 1881.
One of his duties in his first job as resident surgeon at Dr. Steevens's Hospital was to render medical assistance to the victims of the Phoenix Park murders on 6 May 1882.
In 1914, he was recruited (by James Creed Meredith) to help in the importation of guns for the Irish Volunteers with Erskine Childers, Conor O'Brien and others.
On 1 August 1914, 600 Mauser rifles and 20,000 rounds of ammunition were landed at the beach in Kilcoole, County Wicklow in Ireland.
[6] Myles was appointed temporary Lieutenant-Colonel in the Royal Army Medical Corps on 21 November 1914 and also became Honorary Surgeon in Ireland to the King.