William was a younger son of Landgrave Philip of Hesse-Philippsthal from his marriage to Catherine Amalie (1654–1736), daughter of Count Karl Otto of Solms-Laubach.

Wilhelm founded the non-sovereign line Hesse-Philippsthal-Barchfeld of the House of Hesse in 1721, after the death of his father, who had left him Barchfeld and Herleshausen in his will.

Between 1690 and 1732 he built the baroque Wilhelmsburg Castle with three wings, which was named after him, in Barchfeld.

He fought in the Battle of Fontenoy and defended Bergen op Zoom and Mons.

William married on 31 October 1724 in Hoym with Princess Charlotte Wilhelmine (1704–1766), daughter of Prince Lebrecht of Anhalt-Bernburg-Schaumburg-Hoym, with whom he had the following children: