Scion of a large and distinguished noble family, Musin-Pushkin was the son of Count Platon Ivanovich (1698-1745) and Marfa Petrovna Cherkasskaya.
His father had suffered under the reign of Empress Anna Ioannovna, having been falsely accused of disloyalty and underwent a long period of imprisonment and possible torture.
He served as a member of the honor guard at the coronation of Catherine the Great, and in turn was given a high rank in the civil service and rewarded part of the estate that had been confiscated from his father, along with 600 souls to work on it.
A colonel by 1765, he saw active service in the Russo-Turkish War of 1768–1774 under his Father-in-Law General-in-chief Vasily Dolgorukov, commander of the 2nd (Crimean) Field Army.
Nevertheless, Musin-Pushkin continued to be showered with awards for his war service, including the Gold Sword for Bravery, the Order of St. Vladimir, and Diamonds to his St. Andrew's Star.