Karl Philipp was the son of Charles of Nassau-Usingen and Baroness Margareth Maria Magdalena von Biebrich, a title newly created for her.
His father married for the second time the daughter of the mayor of Wiesbaden, Margareth Maria Magdalena Groß (born February 26 1714).
Because she had no title, and the marriage would be considered morganatic, he asked Emperor Joseph II to create the Barony of Biebrich.
In June 1773, his sister Philippa Catherine married Baron Karl Friedrich von Kruse (1738-1806) in the Schloss Biebrich.
The Nassau Family Pact was implemented in 1783 by the other six adult members of the House, but Karl Philipp, who was 37, was not invited to be a signatory because of his parents' marriage, which they considered to be morganatic.