[1] Born in Königsberg, Duchy of Prussia, as the fifth and youngest son of Frederick Louis, Duke of Schleswig-Holstein-Sonderburg-Beck and his wife, Duchess Louise Charlotte of Schleswig-Holstein-Sonderburg-Augustenburg (1658-1740).

[1] He was named after the Russian tsar Peter the Great, who stood by proxy as his godfather after Duke Frederick asked him to do so.

It was one of the first family ties established between the Eastern Orthodox Romanov dynasty and Protestant rulers of Europe, predating the German marriages of Peter's own children and nieces.

It had been inherited by his father's older brother, Duke August (1652–1689), and nephew Frederick William I (1682–1719), and was then sold by the latter's widow, Duchess Antoinette Josefa Isnardi di Castello (1692-1762) to Peter August's older brother, Duke Frederick William II (1687–1749), in 1732.

Thus, in time Peter August became the head of this cadet branch of the House of Oldenburg, he was Duke of Schleswig-Holstein-Sonderburg-Beck in name only.