On 10 October 1746 in Hungen, he married his cousin Ulrike Louise (1731–1792), the daughter of Prince Frederick William of Solms-Braunfels.

His prime ministers, Friedrich Karl von Moser and Casimir of Criss tried to resolve the financial problems of Hesse-Homburg Finance rehabilitate, but the mismanagement that led to the formation of an imperial debit commission to oversee the administration of his predecessor, continued.

Frederick Charles claimed to be entitled to the Duchy via his grandmother Louise Elisabeth of Courland.

However, Empress Anna of Russia granted the Duchy to her favourite Ernst Johann von Biron.

Troops from Darmstadt marched in and Landgrave Louis VIII of Hesse-Darmstadt claimed to be Frederick's legal guardian.