Frederick Louis was born in Haus Beck (now part of Löhne), near Ulenburg, Westphalia, Margraviate of Brandenburg, as the son of August Philipp, Duke of Schleswig-Holstein-Sonderburg-Beck and his wife, Countess Marie Sibylle of Nassau-Saarbrücken (1628-1699).

[1] Duke Frederick William I was killed in the Battle of Francavilla in Sicily in 1719, leaving a widow, née Maria Antonia called Antoinette Josepha Isnardi di Castello, Contessa di Sanfré (1692–1762), and two minor daughters.

[1] Maria Antonia shared administration of Beck with her mother-in-law, Duchess Hedwig Louisa of Schleswig-Holstein-Sonderburg-Beck (née Countess of Lippe-Bückeburg-Schaumburg).

[1] In 1671 Frederick Louis became a cornet in the cavalry regiment von Eller in the army of Brandenburg-Prussia.

[3] On 1 January 1685 in Augustenburg, Frederick Louis married his cousin, Princess Louise Charlotte of Schleswig-Holstein-Sonderburg-Augustenburg (1658-1740), daughter of Ernest Günther, Duke of Schleswig-Holstein-Sonderburg-Augustenburg and his wife, Princess Auguste of Schleswig-Holstein-Sonderburg-Glücksburg.