In 1714, Pyotr Saltykov was sent by Peter the Great to France to master the science of navigation and remained there for some 20 years. In 1759, during the Seven Years' War of 1756-1763, he was appointed commander-in-chief of the Russian army and would soon win a victory at Palzig (Battle of Kay) and Kunersdorf.
In 1763, Pyotr Saltykov became commander-in-chief of Moscow and put in charge of the Moscow Senate Office (Московская сенатская контора). During Saltykov's term, they established a number of new post offices, restored Golovinsky and Kolomensky Palaces and a number of city gates. They also repaired most of the worn-out bridges across the Moscow River and continued dismantling the walls of the White City (fortification belt around Moscow) in order to provide building material for the construction of the Orphanage (Воспитательный дом) (ordered by Catherine the Great) and restoration of the Arsenal. In April 1764, Saltykov reported to Saint Petersburg about the opening of the Moscow Orphanage. With the purpose of providing Muscovites with food, Pyotr Saltykov banned the removal of imported bread from the city and arranged wholesale purchases of bread from landowners. He also secured regular wine deliveries to Moscow, the need for which had been estimated at 575,000 vedros. Saltykov was also fighting against gambling.
In 1765, he took part in burning of books "harmful to society" at the order of Catherine II of Russia. During the plague outbreak in 1771, which caused mass departure of landowners, city officials, and rich merchants from Moscow, Pyotr Saltykov asked Catherine the Great for a permission to leave the city. Without waiting for her reply, he left for his Marfino estate in the outskirts of Moscow. After the Plague Riot had broken out in Moscow on 16 September, Saltykov returned to the city. However, Catherine the Great relieved him of his post on 13 November 1771.