Anatomist. Born in Glasgow, the son of poet and songwriter Dugald MacPhail (1818-87), MacPhail was educated at the University of Glasgow. He was appointed Dean of the Faculty of Medicine at St. Mungo's College in 1900 and, in the same year was elected a Fellow of the Royal College of Physicians and Surgeons of Glasgow. He accepted a lectureship in anatomy at Charing Cross Hospital and King's College in London in 1907, moving to St. Bartholomew's Hospital in 1912 and the Ministry of Health in 1921, as H.M. Inspector of Anatomy for England and Wales. He had served as a Captain in the Royal Army Medical Corps during the First World War. In addition to the Chair in Anatomy at St. Mungo's College, he was honoured with the appointment of Professor of Anatomy at the Royal Academy of Arts in 1934.
He served as Vice-President of the Anatomical Society of Great Britain and Ireland, and had been an examiner in anatomy for several universities, including Aberdeen, Glasgow and St. Andrews.
An enthusiast for the importance of practical anatomical training as part of medical studies, he left instructions that his body should be dissected in Oxford, where the professor had been his friend.