Leonard was ordained to the priesthood for the Diocese of Pittsburgh by Bishop Hugh C. Boyle on June 16, 1935. His first assignment was as assistant chaplain at Mercy Hospital in Pittsburgh, where he remained for two years. From 1937 to 1950, he was resident chaplain of Allegheny County Home and Woodville State Hospital.
Leonard was consecrated to the priesthood for the Diocese of Pittsburgh by Bishop Hugh C. Boyle on June 16, 1935. His initial role was as an assistant chaplain at Mercy Hospital in Pittsburgh, a position he maintained for two years. From 1937 to 1950, he served as the resident chaplain at Allegheny County Home and Woodville State Hospital.