Damian Hartard von der Leyen-Hohengeroldseck was the younger brother of Karl Kaspar von der Leyen-Hohengeroldseck, who was Archbishop of Trier from 1652 to 1676. In 1654, Karl Kaspar arranged for Damian Hartard to be made Archdeacon of Karden and provost of the Stift St. Kastor in Karden. He was ordained as a priest at this time.
On July 3, 1675, the cathedral chapter of Mainz Cathedral elected Damian Hartard as the new Archbishop of Mainz. The cathedral chapter of Worms Cathedral also selected him as the new Bishop of Worms on July 12, 1675, thus continuing the personal union between the Archbishopric of Mainz and the Bishopric of Worms that had existed since 1663. Pope Clement X confirmed both appointments on February 24, 1676.
He was consecrated as a bishop on September 8, 1676 and installed as Bishop of Worms on October 31, 1676. He purchased Neuerburg for his family in 1678. During his reign, the eastern block of the Electoral Palace Mainz was completed.
He is buried in Mainz Cathedral.