Until the age of 14, he lived and was educated at the court of Holstein. He was proclaimed official heir to the Russian throne on November 7, 1742, by his aunt, Elizaveta Petrovna.

On August 21, 1745, Peter Feodorovich married Princess Sophia Augusta Frederica of Anhalt-Zerbst, who was christened into the Orthodox faith as Ekaterina Alexeevna (the future Catherine the Great ).

Peter ascended the Russian throne on December 25, 1761, the day Empress Elizaveta Petrovna died.

His first action was an amnesty for and return from exile of state figures arrested by Elizaveta after her accession.

During his short reign, he introduced various reforms, banned the persecution of dissenters, dissolved the Privy Council and by special decree released the gentry from compulsory state service.

On June 28, 1762, he was overthrown by a court coup led by his wife. After his deposition, he was imprisoned in Ropshinskii Castle, where on July 7, 1762, he was killed by Count Alexei Orlov, Catherine's favorite and one of the organizers of the coup.

He had two children from his marriage with Catherine: a son, later Emperor Paul I, and a daughter, who died in infancy.

Peter III was buried in the Annunciation Church of the Alexander Nevsky Monastery but in December 1796, by order of his son Paul I, his remains were reburied with full honors in the Cathedral of the St. Peter and St. Paul fortress in St. Petersburg.