 He was the third of the six sons of John McNeill, laird of Colonsay and Oronsay (1767–1846) and his wife, Hester McNeill (died 1843).He was the younger brother of the law lord Duncan McNeill, 1st Baron Colonsay and Oronsay.He studied medicine at the University of Edinburgh, where he graduated as a Doctor of Medicine in 1814, at the age of nineteen.