William was the son of Landgrave Henry III from the House of Hesse and his wife Anna of Katzenelnbogen.

When his father died in 1483, William was still a minor, and therefore had his uncle Archbishop Herman IV of Cologne, and Hans Hofman of Dörnberg acted as guardian until 1489.

William died young after he fell from a horse while hunting, and left no legitimate offspring.

His holdings fell to his cousin William II, so that all of the Landgraviate of Hesse was again united in one hand, plus the County of Katzenelnbogen.

However, this last inheritance was disputed by his sister Elisabeth of Hesse-Marburg, triggering the War of the Katzenelnbogen Succession.