Although he was born in New York, Daniel Rooney was raised by a relative in Ireland after his mother died during childbirth of another child, when Daniel was five years old. He began studying for the priesthood at Saint Michael’s College in County Louth, Ireland, and then went to Rome, Italy, to study at the Institute of Charity novitiate . He and other students and priests were forced to leave Italy when World War II began, and since he had retained his American citizenship, he was able to return with little difficulty. He was ordained a Catholic priest in August 1943, in Corpus Christi Church in Galesburg, marking the first ordination of a priest in that city. He served as a member of Corpus Christi High School and also as an assistant pastor of Corpus Christi Church. He later went on to serve at Saint Mary’s Church in Canton, and then Saint Mary’s Church in Champaign. While in Champaign, he also served as chaplain at Mercy Hospital in Urbana until he entered military service and was commissioned a U.S. Army chaplain during the Korean War, where he was twice decorated with the Silver Star, and wounded one time in action.