He was the younger brother of Caroline of Ansbach and thus brother-in-law of George II of Great Britain.

William Frederick was born in Ansbach in 1686 to John Frederick, Margrave of Brandenburg-Ansbach, and his father's second wife; Eleonore Erdmuthe of Saxe-Eisenach.

His two surviving half-brothers, Margraves Christian Albert and George Frederick II, both died unmarried and without legitimate issue.

He married his first cousin, Christiane Charlotte of Württemberg-Winnental in 1709.

[2][3] He died in Unterreichenbach and was succeeded by his son Charles William Frederick, called "The Wild Margrave".