Background
He was the son of van John VI, Count of Nassau-Dillenburg and his third wife Johannetta of Sayn-Wittgenstein. When his father died in 1606, Nassau was divided amongst his five sons. He married in 1617 with Ursula of Lippe, daughter of Simon VI, Count of Lippe.
Career
William Louis received Nassau-Dillenburg, John received Nassau-Siegen, George received Nassau-Beilstein, Ernst Casimir received Nassau-Dietz and John Louis received Nassau-Hadamar. When John Louis was 28 years old, the Thirty Years" War broke out. He tried in vain to keep Nassau-Hadamar out of the war.
Highly indebted, John Louis was forced to sell Esterau to Peter Melander Graf von Holzappel in 1643.
John Louis was much appreciated by the Emperor for his diplomatic skills. In 1638 he successfully led the peace negotiations in Cologne and Munster.
In 1645 he was added to the Imperial delegation under Maximilian von und zu Trauttmansdorff who negotiated the Peace of Westphalia. By 1647 he had replaced Trauttmansdorff as head of the Imperial delegation, and it was he who finalized the treaty.
Ferdinand III, Holy Roman Emperor made him a Prince (Fürst) and gave him a large sum of money.