Allied to Napoleon I of France, Louis in 1806 was elevated to the title of a Grand Duke of Hesse and joined the Confederation of the Rhine, leading to the dissolution of the Empire.

In France he met, among others, the French philosophers Jean le Rond d'Alembert and Denis Diderot, who were some of the prominent figures of the Age of Enlightenment, and editors of the first modern encyclopedia.

In 1773 he traveled with the German-born French writer and critic Friedrich Melchior Grimm to the court of Frederik the Great in Prussia, where his sister Frederica Louisa was married to the heir presumptive Frederick William.

Finally, he traveled on to Russia, where in 1773 he attended the wedding of his second sister Wilhelmina Louisa in St. Petersburg to the heir to the Russian throne, Grand Duke Paul.

The engagement was broken off so that Sophia Dorothea could marry Louis's recently widowed brother-in-law Tsarevich Paul Petrovich, son and heir of Catherine II "the Great", Empress of Russia.

Allied to Napoleon I of France, Louis was elevated to the title of a Grand Duke of Hesse in 1806 and joined the Confederation of the Rhine, leading to the dissolution of the Empire.