Frederick Louis was born in Beck (now part of Löhne), Principality of Minden, Brandenburg-Prussia. He was only the "titular" duke, because he did not inherit the domain of Beck. It had been inherited by Duke Frederick William I, the son of his elder brother, Duke August, in 1689. Duke Frederick William I was killed in the Battle of Francavilla in Sicily in 1719, leaving a widow, "née" "Doña" Maria Antonia Isnardi di Castello, Contessa di Sanfré (1692–1762), and two minor daughters. Maria Antonia shared administration of Beck with her mother-in-law, Duchess Hedwig Louisa of Schleswig-Holstein-Beck ("née" Countess of Lippe-Buckeburg-Schaumburg).