De Lacy Evans O'Leary (1872–1957) was a British Orientalist who lectured at the University of Bristol and wrote a number of books on the early history of Arabs and Copts.

On his father's side, O'Leary was descended from Irish Catholics of Limerick, and included one of the generals in Wellington's Peninsular Campaign.

[1][a] Brought up as a Protestant and educated at Bristol Grammar School, O'Leary converted to Roman Catholicism in about 1888 and began to train for the priesthood at Prior Park College near Bath, before returning to the Church of England in 1890.

During World War I he was Captain-Chaplain of the university's Officer Training Corps and in 1916 served as a chaplain to the British Expeditionary force in Egypt.

[1] After World War II he retired from his parish and went to live in Weston-super-Mare with his sister, although he continued to visit the university occasionally.