Born in Stanorlar, Co. Donegal, on October 13, 1924,  one of two sons and three daughters in the family of Vincent P. McMullin, a solicitor and his wife Carmel (nee Farrell), a medical doctor. His father was a native of Donegal town, from where two of his uncles had gone on for the diocesan priesthood; his mother was from Portarlington in Co. Laois.

• Educated at Maynooth College in Ireland, where he received an undergraduate degree in physics and a bachelor of divinity degree in theology.^[2]
• 1949 ordained a Roman Catholic priest.
• Studied theoretical physics on a fellowship at the Dublin Institute for Advanced Studies
• 1954 earned a Ph.D. in philosophy at the University of Leuven.
• 1954 Joined Notre Dame faculty as an assistant professor of philosophy,
• 1967 a full professor
• 1984 named to the John Cardinal O’Hara Chair.
• 1965-1972 chaired the Notre Dame department of philosophy.

In June 1973, the Donegal Democrat reported as follows:

For many years at commencement exercises. Notre Dame University, Indiana. U.S.A.. has presented its faculty award to a person, who has rendered distinguished service to the University. Last week. Rev. Ernan McMullin. eldest son of the late Mr. and Mrs. V. P. McMullin, Stranorlar, was awarded this signal honour as a tireless scholar, teacher and administrator whose influence internationally has been as great as his impact on the University. A specialist in the philosophy of Science, he and his work are well known and respected on campuses from Berkeley to Moscow, from Georgetown to Capetown. He has been president of the American Catholic Philosophical Association, and is a familiar figure in the corridors of the National Science Foundation. Author or editor of major works on the concept of matter and Galileo, he went to Notre Dame in 1954 from Donegal. In Notre Dame he has been a brilliant Professor of Philosophy, and for seven years a hardworking chairman of that department.