D'Arcy was a third generation Australian, born at Greendale, Ballan, Victoria, where his grandfather Thomas D'Arcy came from Killarney, Co Kerry, Ireland and settled in 1848. His father Patrick was Thomas's second son and his mother was a Macgillicuddy, a member of the chief clan in the same part of Ireland. He was educated at St Patrick's College, Ballarat and then went to Ireland, became a novice in the Redemptorist Order and studied at University College, Dublin. Finding however that he had no true vocation for the religious life D'Arcy went back to Australia and studied medicine at St Vincent's Hospital, graduating at Melbourne University in Arts (1920) and in medicine (1923). He proceeded to the higher degrees in medicine and surgery, after serving as private assistant to Dr Tom Ryan at Nhill, Victoria. He came to London for postgraduate work and took the Fellowship in 1931; he was also a fellow of the Royal Australasian College of Surgeons. He went into private practice at Toorak Road, South Yarra and later at 7 Darling Street there. He was elected to the surgical staff of St Vincent's Hospital in 1933, and became a surgeon to the hospital in 1940, and ultimately consulting surgeon. His consulting rooms were at 33 Collins Street, Melbourne. D'Arcy married in 1934 Julia McCormack MA, who survived him with their son and six daughters. He was a short, thick-set, strong man. While leading the busy life of a successful surgeon in the city, he was a country man at heart who farmed his own land. He was a good naturalist, with a deep knowledge of the wild life of bush and sea-shore. He was also a scholar, a lover of good literature, and widely read in medical literature. He fell from his tractor on his farm at Greendale on 20 December 1966, was picked up unconscious, and died in hospital four months later on 24 April 1967 aged 72, from the effects of a subdural haemorrhage.