After qualifying as M.B., C.M., at Glasgow University in 1895, he gained experience as a surgeon on s.s. Pegu before settling down in Wallsend. Though carrying on an extensive general practice, he found time to interest himself in diseases of the throat and ear and became attached to the Throat, Nose and Ear Hospital, Newcastle upon Tyne. In 1911, he decided to devote all of his time to the speciality, becoming a Senior Surgeon at the hospital and also an Aural Surgeon to the Infectious Diseases Hospital, Newcastle.
During the early years of the Great War, he was heavily involved in the formation of the Tyneside Scottish Battalion, acting as their Medical Officer for a considerable time. In the excellent book 'Tyneside Scottish', by Stewart and Sheen, MacLay is mentioned on a couple of occasions, specifically in relation to commenting on the small amount of venereal disease among the men of the Tyneside Scottish battalions (between one and two per cent!!!) and the fact that on a forced march from Newcastle to Morpeth, not a single man had dropped out, with Dr. MacLay bringing up the rear in his empty medical cart.
A keen golfer, he also enjoyed walking and fishing in Northumbria.
Following his death, Sir Thomas Oliver described him thus, "calm and deliberate in his manner, and a man of few words, Neil MacLay, by his sincerity, readily gained the confidence of his patients as well as the esteem of his medical brethren. He was a man of high principle and had a strong sense of duty".