His parents were
Louis II of Nassau-Weilburg (died: 8 November 1627 in
Saarbrücken) and Landgravine
Anna Maria of Hesse-Kassel (1567–1626). His father had in 1605 re-united all the possessions of the
Walram line of the House of Nassau. After his education at
Metz from 1609 to 1614 he made a
Grand Tour of France, the Netherlands and England. In 1616 William Louis became co-regent with his father. His father died in 1627 and he became guardian of his two youngest brothers, Otto and
Ernest Casimir. On 29 January 1629 in Ottweiler, the inheritance was split and William Louis received the
County of Saarbrücken, the
herrschaft of
Ottweiler, the Bailiwick of
Herbitzheim, and the Community of
Saarwellingen. His brother
John received
Idstein,
Wiesbaden and
Sonnenberg. William Louis remained Regent of Wehen and the district of
Burgschwalbach, the territories of his two youngest brothers, as they were still minors. Shortly thereafter, on 2 March 1629, Emperor
Ferdinand II issued the
Edict of Restitution, by which church property that had been confiscated after 1552 under the
Peace of Passau, was returned to its previous owner. Based on this Edict, the
Prince Bishops of Mainz and Trier claimed substantial parts of the possessions of the Nassau brothers. The Court of Appeal ruled on 7 July 1629 in a dispute between Lorraine and Nassau, that the city and county of
Saarwerden and
Bockenheim and Wieberstweiler were fiefs of Metz and should therefore be returned to Lorraine, and the Nassau family could keep the rest of their county. The Duke of Lorraine, however, took possession of the whole of the County of Saarwerden and the Lordship of Herbitzheim. William Louis appealed, and his appeal was acknowledged on 27 July 1630 by Superintendent Abraham Staymle at Strasbourg. William Louis took the case to the Imperial Council of Princes in
Regensburg and demanded the imperial investiture on 23 July 1631 (although he had refused to join the Catholic League, or to provide troops). Late in 1631, King
Gustavus Adolphus of Sweden and his army arrived at the Rhine. William Louis and his brothers joined him, thereby declaring war on the Emperor. William Louis himself served as a lieutenant colonel in the cavalry regiment of Rhinegrave
Otto Louis of Salm-Kyrburg-Mörchingen and fought with them in the Upper Rhine Valley. King Gustavus Adolphus was killed on 16 November 1632 (6 November according to the Julian Calendar which was still used in Sweden at the time). The Protestant estates then met in
Heilbronn. At this meeting, the three Nassau brothers joined the Swedish side, which was led by chancellor
Axel Oxenstierna. The youngest brother, Count Otto, died on 26 November 1632 and on 11 December Count Ernest Casimir came of age. The Nassau territories were divide anew. Ernest Casimir chose the districts of
Weilburg,
Gleiberg, Mehrenberg and the districts of
Kirchheim and Stauf, that had previously belonged to Otto. The district of
Usingen and the Lordship of
Stockheim were divided. In August 1633, the Swedish army attacked form the Alsace into the County of Saarwerden, which was still occupied by Lorraine. The county was conquered, but not given back to the Nassaus. On 5 September 1633, their representative Count John of Nassau-Idstein, signed an alliance with France against the Emperor. In March 1634 William Louis was at the meeting in Frankfurt, where Oxenstierna tried to win over the Electors of Saxony and Brandenburg to join the
Heilbronn League. Here, the Nassau brothers also reached a compromise with the
Lords of Geroldseck about the ownership rights to
Lahr. On 7 June William Louis sealed the alliance with France. The negotiations in Frankfurt came to an abrupt end when Emperor
Ferdinand II won the
Battle of Nördlingen on 6 September 1634. As the imperial army of the Middle Rhine approached, the counts brought their archives to a secure place in Frankfurt and then proceeded to Kirchheim. They had to give up their possessions of the right bank of the Rhine. After the death of Rhinegrave Otto Louis, William Louis entered the service of Duke
Bernard of Saxe-Weimar. They launched a campaign to
Wetterau and attacked a division of the Imperial General Count von Mansfeld at
Michelstadt on the 24 December 1634 In 1635, he returned to Frankfurt to attend a meeting of the Protestant states and their allies. At this meeting, it was decided that Sweden would return Saarwerden to the Nassaus. On 23 April 1635 the family fled to
Bockenheim, where the counties of Nassau-Saarbrücken and Saarwerden should have been handed over. However, on 30 May 1635 a number of imperial estates, including the Electorates of Brandenburg and Saxony, had concluded the
Peace of Prague and the Nassau Counts were expressly excluded from this agreement. They then went to Saarbrücken, which was defended by
Bernard of Saxe-Weimar. Bernard was defeated in August 1635 during an attack on Frankfurt and had to retreat to Metz. William Louis and Ernest joined him; John chose to go into exile in Strasbourg. However, a panic broke out in Saarbrücken as the Imperial troops under
Matthias Gallas approached and a large number of people tried to flee. The count's family decided that under the circumstance, Strasbourg was too far and could not be reached. So they followed the advice of King
Louis XIII and fled to the free imperial city of
Metz on 16 June 1635. In November 1635 the imperial commissioner
Bertram von Sturm appeared in the Nassau lands of and declared the three brothers and had forfeited their counties and all their possessions. The Emperor gave the Duke of Lorraine the counties of Saarbrücken and Saarland and the bailiwick of Herbitzheim and the fortress of
Homburg on the Blies as a reward for services rendered. In 1636, the brothers attempted to petition the Emperor for an imperial pardon; the Elector of Saxony mediated. This attempt failed, but it wasn't until 1637 that the counts were told the reasons for this imperial wrath. Only in 1639 did William Louis and Ernest receive a pass that enabled them to represent their cause in Vienna in person. William Louis died on 22 August 1640 in Metz and was buried in a pauper's grave. His widow returned with the children to Saarbrücken in 1643. His three sons participated in a new division of the Nassau territories on 31 March 1659.
Registrar Andreae completed William Louis's genealogy books, a project his father
Louis II had begun. Some works of the painter
Henrich Dors from
Altweilnau were commissioned by William Louis. == Marriage and issue ==