[1] He was a son of Ernest I of Hesse-Rheinfels-Rotenburg (1623-1693) and his wife, Countess Maria Eleonore of Solms-Lich (1632-1689).

After his father's death in 1693, William ruled one half of the Rotenburg Quarter, the quarter of Hesse-Kassel which Landgrave Maurice of Hesse-Kassel had distributed as fiefs among the sons of his second wife, Juliane.

He officially resided in Rotenburg an der Fulda, but he often stayed in Langenschwalbach in the Taunus area.

William's dominions included the lower part of the County of Katzenelnbogen and the districts and castles of Burg Rheinfels, Reichenberg and Hohenstein as well as shares of Umstadt and Vierherren an der Lahn.

William died in 1725 and was buried in the Catholic Church of St. Elizabeth in Langenschwalbach.