He is a son of Nikolaus, Hereditary Grand Duke of Oldenburg and Princess Helena of Waldeck and Pyrmont.
Frederich August is the sixth child and fourth son of Nikolaus, Hereditary Grand Duke of Oldenburg and his first wife Princess Helena of Waldeck and Pyrmont.
His paternal grandparents are Frederick Augustus II, Grand Duke of Oldenburg and Duchess Elisabeth Alexandrine of Mecklenburg-Schwerin.
Friedrich August's first wife was Princess Marie Cécile of Prussia, a daughter of Louis Ferdinand, Prince of Prussia (second son of William, German Crown Prince) and his wife, Grand Duchess Kira Kirillovna of Russia.
On 9 February 1991, Friedrich August was remarried to Donata Countess of Castell-Rüdenhausen in Rüdenhausen, Germany.