Wilhelm Christian Karl, 3rd Prince of Solms Braunfels (9 January 1759, in Braunfels – 20 March 1837, in Braunfels) was by succession an immediate Prince, then a nobleman and head of the Princely House of Solms-Braunfels, a Prussian major general and Hessian deputy.
William was a member of the Princely House of Solms-Braunfels. His grandfather Frederick William (1696–1761) was the first Prince of Solms-Braunfels. His parents were the imperial colonel and lieutenant general of the United Provinces Ferdinand Wilhelm Ernst (1721–1783) and Countess Sophie Christine Wilhelmine of Solms-Laubach. first daughter and second child of Christian August, Count of Solms-Laubach. Prussian Major General Frederick William (1770–1814) was one of his younger brothers.
On 6 October 1792, he married Wild- und Rheingräfin Auguste of Salm-Grumbach (1771–1810) half-sister of Friedrich, Prince of Salm-Horstmar. They had four children:
- Wilhelmine (1793–1865) ∞ Alexius, Prince of Bentheim and Steinfurt (1781–1866) and had issue
- Sophie Auguste (1796–1855) ∞ Johann August Karl, Prince of Wied (1779–1836) and had issue; they were the paternal grandparents of Queen Elisabeth of Romania
- Ferdinand, 4th Prince of Solms-Braunfels (1797–1873) ∞ Countess Ottilie of Solms-Laubach (1807–1884), without issue
- Karl Wilhelm Bernhard (1800–1868), General of Cavalry
By his maitresse Anna Elisabeth Becker (1779–1852), whom he married morganatically once widower, he had three children who received patronymic Wilhelmi